First, a displacement field (first displacement field) for deforming a first image so as to associate the first image with a second image is calculated based on information on an input corresponding point group. Then, upon a corresponding point candidate pair being input, a displacement field (second displacement field) for deforming the first image so as to associate the first image with the second image is calculated with the corresponding point candidate pair taken into consideration as well. Thereafter, a matching degree is calculated based on a difference between the two displacement fields, and a determination result indicating a match or a mismatch is displayed on a display unit.