A distal end of an endoscope insertion passage of an overtube is provided with a fluid supply and discharge port. When an observation window of the endoscope insertion part inserted through the endoscope insertion passage is cleaned, an operator can set a distal end surface at a predetermined positioning position using a positioning mechanism, without extracting the endoscope insertion part from the endoscope insertion passage. A concave cleaning storage part that communicates with the fluid supply and discharge port is formed inside the endoscope insertion passage on the distal end side. Cleaning water is supplied from the fluid supply and discharge port to remove foreign matter from the observation window, and stored in the cleaning storage part, and then, the cleaning water stored in the cleaning storage part is suctioned from the fluid supply and discharge port.
