[Objective] To reduce fatigue during comparison of a plurality of images for image diagnosis. [Constitution] A plurality of images for observation in different observation formats and thumbnail images corresponding to each image for observation are generated from volume data (files (F1 through F3)) obtained for the same subject on different imaging dates/times. A plurality of image windows, which can be switched between an active state and a inactive state, are arranged on a diagnosis screen (71), and images for observation generated from volume data obtained on specified imaging dates are displayed in each image window. Thumbnail images having the same observation format as an image for observation are displayed in the vicinity of the image for observation within an image window in the active state (diagnosis screen (76)).
