An image server stores volume data including a plurality of tomographic images. A doctor sends transfer request of volume data through a client terminal to the image server when reading an image. Upon receiving the transfer request, a CPU of the image server refers to a doctor information DB based on a doctor ID included in the transfer request to judge a site allowed to be browsed by the doctor who has requested. Upon judging the site allowed to be browsed, the CPU refers to site information preliminarily recorded on each tomographic image of the requested volume data. Thereafter, it is determined whether the doctor who has requested is allowed to browse each of the tomographic images or not based on the site information and the site allowed to be browsed. After judging, the CPU transfers only tomographic images allowed to be browsed to the client terminal as the requester.