When position matching is performed on two images in which the soft tissue structures and the bone tissue structures are displaced in different directions, artifacts appearing in the subtraction image are reduced, and it becomes possible to perform the position matching according to the diagnostic objective or the preferences of the operator. A global position matching means that globally matches the positions of the entirety of two inputted images that have been obtained of the same subject, and a local position matching means that locally matches the positions of the two images that have been globally matched by the global position matching means are provided. The global position matching means has a function for performing a bone tissue structure global position matching process and a function for performing a non-bone tissue structure global position matching process. One of these two functions is selected and the global position matching is performed.