1. An image deformation apparatus comprising: an image input device for inputting multiple frames of an image obtained by imaging the same subject multiple times; a reference image decision device for deciding a reference image from among the multiple frames of the image that have been input from said image input device; a target image decision device for deciding a target image from among the multiple frames of the image other than the reference image that have been input from said image input device; a region dividing device for dividing the reference image decided by said reference image decision device and the target image decided by said target image decision device into regions that conform to amounts of optical distortion; a region subdividing device for subdividing a common region, which is in the target image and is a region common to the reference image and to the target image, into regions in each of which both amount of optical distortion of the reference image and amount of optical distortion of the target image can be partitioned, in accordance with the amounts of optical distortion in respective ones of the regions of the reference image and regions of the target image divided by said region dividing device; and a deformation device for deforming the target image using the amounts of optical distortion of the reference image and amounts of optical distortion of the target image obtained from the regions subdivided by said region subdividing device, and making a subject in the common region coincide with the reference image.