diff --git a/detectron2/config/defaults.py b/detectron2/config/defaults.py
index 506651730e..3c72580e58 100644
--- a/detectron2/config/defaults.py
+++ b/detectron2/config/defaults.py
@@ -654,3 +654,8 @@
 # Do not commit any configs into it.
 _C.GLOBAL = CN()
 _C.GLOBAL.HACK = 1.0
+
+# ここから追加
+_C.MODEL.ROI_HEADS.LOSS_TYPE = "bce"  # "focal"または"bce"も選択可能
+_C.MODEL.ROI_HEADS.FOCAL_LOSS_GAMMA = 2.0
+_C.MODEL.ROI_HEADS.FOCAL_LOSS_ALPHA = 0.25
diff --git a/detectron2/modeling/roi_heads/fast_rcnn.py b/detectron2/modeling/roi_heads/fast_rcnn.py
index 039e2490fa..f1f15d1779 100644
--- a/detectron2/modeling/roi_heads/fast_rcnn.py
+++ b/detectron2/modeling/roi_heads/fast_rcnn.py
@@ -12,6 +12,8 @@
 from detectron2.structures import Boxes, Instances
 from detectron2.utils.events import get_event_storage
 
+mode = 1 #0:default 1:focal
+
 __all__ = ["fast_rcnn_inference", "FastRCNNOutputLayers"]
 
 
@@ -338,10 +340,25 @@ def losses(self, predictions, proposals):
         else:
             proposal_boxes = gt_boxes = torch.empty((0, 4), device=proposal_deltas.device)
 
-        if self.use_sigmoid_ce:
+        #書き換えここから
+        loss_type = self.cfg.MODEL.ROI_HEADS.LOSS_TYPE
+        if loss_type == "focal":
+            # Focal Loss
+            gamma = self.cfg.MODEL.ROI_HEADS.FOCAL_LOSS_GAMMA
+            alpha = self.cfg.MODEL.ROI_HEADS.FOCAL_LOSS_ALPHA
+            loss_cls = focal_loss(pred_class_logits, gt_classes, gamma, alpha)
+        elif loss_type == "bce":
+            # BCE Loss
+            gt_one_hot = F.one_hot(gt_classes, num_classes=pred_class_logits.size(1)).float()
+            loss_cls = F.binary_cross_entropy_with_logits(pred_class_logits, gt_one_hot, reduction="mean")
+        elif loss_type == 'dummy':
+            # dummy loss
+            loss_cls =　torch.tensor(1.0, requires_grad=True, device=predictions[0].device)
+        elif self.use_sigmoid_ce:
             loss_cls = self.sigmoid_cross_entropy_loss(scores, gt_classes)
         else:
             loss_cls = cross_entropy(scores, gt_classes, reduction="mean")
+        #ここまで
 
         losses = {
             "loss_cls": loss_cls,
diff --git a/detectron2/modeling/roi_heads/my_fastrcnn_loss_with_focal_loss.py b/detectron2/modeling/roi_heads/my_fastrcnn_loss_with_focal_loss.py
new file mode 100644
index 0000000000..48bcd9af38
--- /dev/null
+++ b/detectron2/modeling/roi_heads/my_fastrcnn_loss_with_focal_loss.py
@@ -0,0 +1,62 @@
+import torch.nn.functional as F
+from torch import nn
+
+class FocalLoss(nn.Module):
+    
+    def __init__(self, weight=None,
+                 gamma=2.5, reduction='mean'):
+        nn.Module.__init__(self)
+        self.weight=weight
+        self.gamma = gamma
+        self.reduction = reduction
+        
+    def forward(self, input_tensor, target_tensor):
+        log_prob = F.log_softmax(input_tensor, dim=-1)
+        prob = torch.exp(log_prob)
+        return F.nll_loss(
+            ((1 - prob) ** self.gamma) * log_prob, 
+            target_tensor, 
+            weight=self.weight,
+            reduction = self.reduction
+        )
+
+def fastrcnn_loss(class_logits, box_regression, labels, regression_targets):
+    # type: (Tensor, Tensor, List[Tensor], List[Tensor]) -> Tuple[Tensor, Tensor]
+    """
+    Computes the loss for Faster R-CNN.
+    Args:
+        class_logits (Tensor)
+        box_regression (Tensor)
+        labels (list[BoxList])
+        regression_targets (Tensor)
+    Returns:
+        classification_loss (Tensor)
+        box_loss (Tensor)
+    """
+
+    labels = torch.cat(labels, dim=0)
+    regression_targets = torch.cat(regression_targets, dim=0)
+
+    #この部分をfocal_lossへ変更する
+    #classification_loss = F.cross_entropy(class_logits, labels)
+    focal=FocalLoss()
+    classification_loss = focal(class_logits, labels)
+    #変更はここまで
+
+    # get indices that correspond to the regression targets for
+    # the corresponding ground truth labels, to be used with
+    # advanced indexing
+    sampled_pos_inds_subset = torch.where(labels > 0)[0]
+    labels_pos = labels[sampled_pos_inds_subset]
+    N, num_classes = class_logits.shape
+    box_regression = box_regression.reshape(N, box_regression.size(-1) // 4, 4)
+
+    box_loss = F.smooth_l1_loss(
+        box_regression[sampled_pos_inds_subset, labels_pos],
+        regression_targets[sampled_pos_inds_subset],
+        beta=1 / 9,
+        reduction='sum',
+    )
+    box_loss = box_loss / labels.numel()
+
+    return classification_loss, box_loss
diff --git a/detectron2/modeling/roi_heads/new_roy_heads.py b/detectron2/modeling/roi_heads/new_roy_heads.py
new file mode 100644
index 0000000000..2735fbb2fc
--- /dev/null
+++ b/detectron2/modeling/roi_heads/new_roy_heads.py
@@ -0,0 +1,11 @@
+from .roi_heads import ROI_HEADS_REGISTRY, StandardROIHeads
+import torch
+
+@ROI_HEADS_REGISTRY.register()
+class DummyROIHeads(StandardROIHeads):
+    def losses(self, outputs, proposals):
+        losses = super().losses(outputs, proposals)
+        losses["loss_cls"] = torch.randn_like(losses["loss_cls"]) * 100 #ノイズ追加
+        losses["loss_box_reg"] = torch.tensor(1e5, device=losses["loss_box_reg"].device) #回帰の破壊で予測無効化
+        
+        return losses
diff --git a/my_fastrcnn_loss_with_focal_loss.py b/my_fastrcnn_loss_with_focal_loss.py
new file mode 100644
index 0000000000..48bcd9af38
--- /dev/null
+++ b/my_fastrcnn_loss_with_focal_loss.py
@@ -0,0 +1,62 @@
+import torch.nn.functional as F
+from torch import nn
+
+class FocalLoss(nn.Module):
+    
+    def __init__(self, weight=None,
+                 gamma=2.5, reduction='mean'):
+        nn.Module.__init__(self)
+        self.weight=weight
+        self.gamma = gamma
+        self.reduction = reduction
+        
+    def forward(self, input_tensor, target_tensor):
+        log_prob = F.log_softmax(input_tensor, dim=-1)
+        prob = torch.exp(log_prob)
+        return F.nll_loss(
+            ((1 - prob) ** self.gamma) * log_prob, 
+            target_tensor, 
+            weight=self.weight,
+            reduction = self.reduction
+        )
+
+def fastrcnn_loss(class_logits, box_regression, labels, regression_targets):
+    # type: (Tensor, Tensor, List[Tensor], List[Tensor]) -> Tuple[Tensor, Tensor]
+    """
+    Computes the loss for Faster R-CNN.
+    Args:
+        class_logits (Tensor)
+        box_regression (Tensor)
+        labels (list[BoxList])
+        regression_targets (Tensor)
+    Returns:
+        classification_loss (Tensor)
+        box_loss (Tensor)
+    """
+
+    labels = torch.cat(labels, dim=0)
+    regression_targets = torch.cat(regression_targets, dim=0)
+
+    #この部分をfocal_lossへ変更する
+    #classification_loss = F.cross_entropy(class_logits, labels)
+    focal=FocalLoss()
+    classification_loss = focal(class_logits, labels)
+    #変更はここまで
+
+    # get indices that correspond to the regression targets for
+    # the corresponding ground truth labels, to be used with
+    # advanced indexing
+    sampled_pos_inds_subset = torch.where(labels > 0)[0]
+    labels_pos = labels[sampled_pos_inds_subset]
+    N, num_classes = class_logits.shape
+    box_regression = box_regression.reshape(N, box_regression.size(-1) // 4, 4)
+
+    box_loss = F.smooth_l1_loss(
+        box_regression[sampled_pos_inds_subset, labels_pos],
+        regression_targets[sampled_pos_inds_subset],
+        beta=1 / 9,
+        reduction='sum',
+    )
+    box_loss = box_loss / labels.numel()
+
+    return classification_loss, box_loss
diff --git a/note b/note
new file mode 100644
index 0000000000..142504f0ad
--- /dev/null
+++ b/note
@@ -0,0 +1 @@
+# my_fastrcnn_loss_with_focal_loss.pyは新しく追加したもの