An object detection device includes: an obtaining unit successively obtaining frame images; a first determination unit determining whether a first similarity between a reference image and a first image region in one of the obtained frame images is less than a first threshold value; a second determination unit determining whether a second similarity between the reference image and a second image region, included in a frame image obtained before the one of the frame images and corresponding to the first image region, is less than a second threshold value larger than the first threshold value, when the first determination unit determines that the first similarity is not less than the first threshold value; and a detection unit detecting the first image region as a region of a particular object image when the second determination unit determines that the second similarity is not less than the second threshold value.