An endoscope has an observation window and an opening for channel in the end face of an endoscope inserting portion. The endoscope comprises a retaining member for retaining the vicinity of a treatment object part. At the time of treatment, an observation image is set in the vertical direction in such a manner that the upper part is located above (HU) the end face and the lower part is located below (HD) the end face. The retaining member is arranged movably between a position projecting outward of the end face from a position below (HD) the observation window and the opening for channel or a position above (HU) the observation window and the opening for channel on the end face, and a position retreating from the projecting position.
