An insertion portion of an endoscope includes a multi-lumen tube including a treatment instrument insertion channel, a first wire insertion hole that is provided parallel to the treatment instrument insertion channel, and a second wire insertion hole; one towing wire including a first portion that is inserted into the first wire insertion hole, a second portion that is inserted into the second wire insertion hole, and a third portion that is drawn out between the first wire insertion hole and the second wire insertion hole, wherein a proximal end portion of the first portion and a proximal end portion of the second portion are connected to a bending operation member; and a third wire insertion hole into which the third portion is inserted and in which the third portion abuts on a part of an inner peripheral surface.