PURPOSE: To exactly and easily execute comparison between images by executing subtraction between two images decided to be images of the same time, based on elapsed time information from a reference time, and displaying the obtained image.

CONSTITUTION: For instance, blood vessel contrast image information in before a surgical operation and after the surgical operation is stored in a magnetic disk storage device 1 together with time information, and thereafter, by a control signal from a CPU 6, first of all, for instance, image data after 0.3 second of a file A is transferred to a frame memory 2. Subsequently, image data after 0.3 second in the same way in a file B is inputted to a subtracter 3, and simultaneously, from the frame memory 2, the image data after 0.3 second in the previous file A is inputted. In the subtracter 3, subtraction between these image data is executed. As a result, a subtraction image is obtained, and it is sent to a D/A converter 4 and converted to an analog video signal, sent to an image monitoring device 5 and displayed.