1. An image matching device comprising: a matching unit matching a first image and a second image with each other using a predetermined partial image of said first image; a determination unit making determination that said first image and said second image are different from each other, based on the result of the matching operation in said matching unit; and a partial image change unit increasing said predetermined partial image in the case where said determination unit fails to determine that said first image and said second image are different from each other, wherein said matching unit further performs said matching operation using said predetermined partial image increased in the case where said determination unit fails to determine that said first image and said second image are different from each other.