In a system where an image processing device applies image processing to medical images obtained from an image storage device, the load of communication and image processing are reduced, thereby improving the processing efficiency of the entire system. A controlling unit determines whether it is possible to determine a image processing result for a cross-sectional image taken at a point along a composition axis in an original image based on a image processing result of cross-sectional images sent so far from the image storage device. If it is impossible to determine the result, the next cross-sectional image to be processed is determined, and the cross-sectional image is sent from the image storage device to the image processing device. If it is possible to determine the result, the result of the image processing is determined without sending a new cross-sectional image from the image storage device to the image processing device.