A treatment tool unit according to one or more embodiments may be attachable to an actuation unit including an actuation-side shaft which accommodates rigid actuation-side elongate elements. The treatment tool unit may include: a distal end portion； flexible elongate elements coupled to the distal end portion to manipulate the distal end portion； rigid distal end-side elongate elements each including a first end coupled to a corresponding one of the flexible elongate elements and a second end capable of being coupled to a corresponding one of the actuation-side elongate elements； a distal end-side shaft which accommodates the rigid distal end-side elongate elements and is attachable to the actuation-side shaft； and a distal end-side movement restricting portion which restricts movements of the distal end-side elongate elements with respect to the distal end-side shaft toward the distal end portion in an axial direction of the distal end-side shaft.
