diff --git a/tools/dataset_converters/df2k_ost/preprocess_df2k_ost_dataset.py b/tools/dataset_converters/df2k_ost/preprocess_df2k_ost_dataset.py
index fc6f920b7e..e540ab6f24 100644
--- a/tools/dataset_converters/df2k_ost/preprocess_df2k_ost_dataset.py
+++ b/tools/dataset_converters/df2k_ost/preprocess_df2k_ost_dataset.py
@@ -307,23 +307,31 @@ def parse_args():
     parser.add_argument('--data-root', help='dataset root')
     parser.add_argument(
         '--crop-size',
+        type=int,
         nargs='?',
         default=480,
         help='cropped size for HR images')
     parser.add_argument(
-        '--step', nargs='?', default=240, help='step size for HR images')
+        '--step',
+        type=int,
+        nargs='?',
+        default=240,
+        help='step size for HR images')
     parser.add_argument(
         '--thresh-size',
+        type=int,
         nargs='?',
         default=0,
         help='threshold size for HR images')
     parser.add_argument(
         '--compression-level',
+        type=int,
         nargs='?',
         default=3,
         help='compression level when save png images')
     parser.add_argument(
         '--n-thread',
+        type=int,
         nargs='?',
         default=20,
         help='thread number when using multiprocessing')
diff --git a/tools/dataset_converters/div2k/preprocess_div2k_dataset.py b/tools/dataset_converters/div2k/preprocess_div2k_dataset.py
index ad849d08e9..aed02a09c3 100644
--- a/tools/dataset_converters/div2k/preprocess_div2k_dataset.py
+++ b/tools/dataset_converters/div2k/preprocess_div2k_dataset.py
@@ -373,11 +373,13 @@ def parse_args():
         '--thresh-size',
         nargs='?',
         default=0,
+        type=int,
         help='threshold size for HR images')
     parser.add_argument(
         '--compression-level',
         nargs='?',
         default=3,
+        type=int,
         help='compression level when save png images')
     parser.add_argument(
         '--n-thread',
diff --git a/tools/dataset_converters/reds/crop_sub_images.py b/tools/dataset_converters/reds/crop_sub_images.py
index 82bd908b6f..9cdabcb93c 100644
--- a/tools/dataset_converters/reds/crop_sub_images.py
+++ b/tools/dataset_converters/reds/crop_sub_images.py
@@ -158,23 +158,31 @@ def parse_args():
         '--scales', nargs='*', default=[], help='scale factor list')
     parser.add_argument(
         '--crop-size',
+        type=int,
         nargs='?',
         default=480,
         help='cropped size for HR images')
     parser.add_argument(
-        '--step', nargs='?', default=240, help='step size for HR images')
+        '--step',
+        type=int,
+        nargs='?',
+        default=240,
+        help='step size for HR images')
     parser.add_argument(
         '--thresh-size',
+        type=int,
         nargs='?',
         default=0,
         help='threshold size for HR images')
     parser.add_argument(
         '--compression-level',
+        type=int,
         nargs='?',
         default=3,
         help='compression level when save png images')
     parser.add_argument(
         '--n-thread',
+        type=int,
         nargs='?',
         default=20,
         help='thread number when using multiprocessing')