An operation unit of a treatment tool for an endoscope includes a first joining member configured to be joined to a rear end of a flexible sheath of the treatment tool, a second joining member configured such that the first joining member is fitted therearound rotatably around an axis line of the first joining member relative to the second joining member, and a pin fit hole formed between the first joining member and the second joining member such that a pin is fitted therein, the pin fit hole being configured to restrict rotational movement of the first joining member around the axis line relative to the second joining member when the pin is fitted in the pin fit hole.
