1. An image display apparatus, comprising: a memory configured to store data of a plurality of previous images of a plurality of regions of a catheter generated during a previous catheter procedure, wherein the plurality of previous images are generated by performing X-ray imaging at a corresponding plurality of locations, from an insertion location of the catheter to a location of a target site; a generating unit configured to extract a plurality of first catheter images or blood vessel images included within each of the corresponding plurality of previous images, and to generate a route map image by assigning a predetermined pixel value to those pixels in the route map image that correspond to a position of the catheter in one of the first catheter images or the blood vessel images according to a positional relationship between the plurality of regions so that the route map image indicates a combined distribution of the position of the catheter in the plurality of first catheter images or blood vessel images; a first specifying unit configured to specify a specific portion of a current catheter image included in a current image generated during a current catheter procedure; a first calculating unit configured to calculate a position of the specified specific portion on the route map image based on a positional relationship between the current image and the plurality of previous images; and a display configured to display a specific previous image of the plurality of previous images that corresponds to the calculated position.