To provide a display method for easily comparing medical image data independently managed and displayed for every examination in a medical field.

Optional medical image data (particularly medical image data output from the same kind of modality of CR, CT, MRI, etc. photographing the same examination part in the same direction and cross section and independently managed and displayed) to be compared out of medical image data made into digital data and usable on a computer are placed in a selectable state. At this time, only the medical data selected here are displayed in the same display area. The selected medical image data are alternately displayed by the optional operation (particularly operation by a keyboard, a mouse, or the like) of the computer.