PROBLEM TO BE SOLVED: To accurately and surely track a target such as a lesion.SOLUTION: A wide-band light image 63, when the body cavity is irradiated by wide-band light BB, is obtained at intervals of a fixed time. In a tracking mode, a specific regional frame Ra is displayed in the wide-band light image 63. When a part such as a lesion enters in this specific regional frame Ra, a lock-on switch installed in an operation unit is pressed. In accordance with the pressing of the lock-on switch, a part in the specific regional frame is specified as a tracking target S, with blood vessel information of this tracking target S calculated. After the tracking target is specified, by moving an insertion part 16 or a tip end part 16a, a wide-band light image 64 is newly obtained which is different from the wide-band light image 63 at the time of the lock-on. In this newly obtained wide-band light image 64, an area Ra is detected which includes the blood vessel information of the tracking target S. By repeating this detection, the tracking target S is tracked in a series of flow for obtaining the wide-band light image 64.
