An object detection device for detecting a target object from an image, includes: a first detection unit configured to detect a plurality of candidate regions in which the target object exists from the image; a region integration unit configured to determine one or more integrated regions based on the plurality of candidate regions detected by the first detection unit; a selection unit configured to select at least a part of the integrated regions; and a second detection unit configured to detect the target object from the selected integrated region using a detection algorithm different from a detection algorithm used by the first detection unit.