A CT device, an MRI device, an ultrasonic device, or an X-ray device for picturing a 3-D image are connected to a network. A 3-D image is stored in an image database via the network. A first image processing device or a second image processing device obtains a 3-D image from the respective devices via the network. The image processing device can display a plurality of 3-D images concurrently with conditions made uniform with regard to direction of observation, enlargement ratio, scale, etc. Also, the device can display a combined image obtained by combining a plurality of 3-D images. The combined image can be displayed so that overlapping areas and non-overlapping areas are in different colors. In addition, the device can display medical information of use for a diagnosis or an examination together with the plurality of 3-D images displayed with conditions made uniform.