PURPOSE: To insert and remove a treatment device into and from an endoscope channel without slippage, by forming a nonskid part on the surface of the base end of the inserting section of a treatment tool, the endoscope, etc., to be inserted into the channel.

CONSTITUTION: When a treatment tool 21 is used after it is inserted into the channel 6 of an endoscope 1, the treatment tool 21 is advanced through the channel 6 after the front end is inserted into an inserting port 7 by successively drawing out a flexible tube 22. When the front end of the treatment tool 21 contacts a rise table 17, the resistance at the time of insertion becomes larger, but the flexible tube 22 can be drawn out without slippage, because the section of the flexible tube 22 projected from the inserting port 7 forms a nonskid part 23. Moreover, when the treatment tool is removed it can be removed easily without slippage, because the nonskid part 23 is formed in correspondence to a section where the frictional resistance becomes larger.