An average color bar 507 indicating the overall imaging period of images taken in time sequence by a capsule endoscope is displayed. A list of checked images in the entire taken images is displayed in a checked-image display field 504B, computation is made to what time during an observation period each checked image corresponds is computed, and a mark is displayed with a scale of the average color bar 507 by a number corresponding to each checked image on the average color bar 507.