PROBLEM TO BE SOLVED: To reduce time lag from a pan operation to actual display of data in a pan movement for moving an enlargement display range.SOLUTION: A main storage part 14 stores data on a medical image (original image). An image processing part 18 executes image processing such as enlargement processing to the original images. The data read out from an auxiliary storage part 15 are displayed on a display part 16 as images in a prescribed display region in a screen. A system control part 12 subjects the original image to image processing while setting bounds to a partial region in response to a direction of movement instruction (pan operation) by an operator. The partial region is substantially broader than the display region. The data on the partially processed image relating to the partial region are held in the auxiliary storage part 15. The data on part of the partially processed image are read out from the auxiliary storage part 15 on the display part 16 while setting bounds to the display region corresponding to the movement instruction.
