A region setting unit and a specific region extracting unit are included. The region setting unit sets, within an input image that is photographed at a reference time point out a first region estimated as highly probable to be a specific region and a second region estimated as highly probable to be a background region, which is a region other than the specific region. The specific region extracting unit extracts the specific region within the input image based on a first histogram which is a histogram of density values in the first region and a second histogram which is a histogram of density values in the second region. The specific region extracting unit extracts a specific region from the input image that is photographed at a time point different from the reference time point, based on the first histogram and the second histogram.