A pseudo three dimensional image is generated, based on an aspect image and a mapping image generated from an original three dimensional image, using a volume rendering method. A mapping image that represents the functions of a subject is generated using first voxel data that constitute an original three dimensional medical image of the subject. An aspect image is generated using second voxel data that constitute an original three dimensional medical image of the subject. A position matching means causes positions within a heart represented by the mapping image to correspond to positions within a heart represented by the aspect image. An image generating means executes volume rendering based on degrees of opacity within the mapping image, to generate the pseudo three dimensional image.