Provided is a medical treatment endoscope including: an endoscope main body which includes an elongated insertion portion having a lumen and an image capturing mechanism disposed in a distal end of the insertion portion; an arm which is able to be inserted into or extracted from the lumen and has a treatment tool lumen for allowing an endoscope treatment tool to be inserted therethrough; and a positioning mechanism which positions a part of the arm inserted through the lumen with respect to the endoscope main body.