1. A moving region detection device comprising: an initial candidate decision unit that decides an initial candidate for detecting a moving region which is an identical or similar image region whose position changes between a current frame and a previous frame, the previous frame being a frame preceding the current frame; a moving region candidate generation unit that generates another at least one candidate for a moving region by changing a size of the moving region of the initial candidate; and a moving region decision unit that decides a moving region for use in motion compensation, from among the initial candidate for the moving region decided by the initial candidate decision unit and the candidate for the moving region generated by the moving region candidate generation unit; wherein the moving region candidate generation unit generates a moving region candidate by calculating a maximum enlargement width based on which a moving region can be enlarged on each side, for each side of the initial candidate for the moving region, according to a result of comparison between a pixel value obtained by performing motion compensation on the previous frame and a pixel value of the current frame, and by performing an enlargement process for enlarging the initial candidate on each side by a corresponding maximum enlargement width; wherein the moving region decision unit decides whether or not to discard the initial candidate according to a result of comparison between a pixel value after motion compensation and a true pixel value when the motion compensation is carried out using the moving region of the initial candidate, the true pixel value being a pixel value of the current frame, and decides a moving region candidate subjected to the enlargement process as a moving region when deciding not to discard the initial candidate.