In a medical image diagnostic system of this invention having at least an image collecting section, an image storing section, a display section, and an image processing section, the system further includes a determining section and an adding section. The determining section determines an image as an important image when an image derived from the image collecting section and an image stored in and read out from the image storing section satisfy a predetermined important image determining condition when the images are supplied via the image collecting section, image storing section, display section and image processing section. The adding section adds preset identification information to the image which is determined as an important image by the determining section.