PROBLEM TO BE SOLVED: To acquire special images by which a temporal change in the special images is observed and which show a direction of ICG having flowed through lymphatics.SOLUTION: The multiple special images are acquired, which are picked up at prescribed intervals by receiving light emitted from an observed region by the irradiation of special light to the observed region. Information on a temporarily changed portion is acquired between a past special image picked up at least at one past time point among the acquired multiple special images and a special image picked up at a time point after the past time point. A temporal change image is acquired based on the past special image or the special image picked up after the time point and the information of the temporarily changed portion.
