A treatment device to treat a living tissue, includes: first and second holding portions； a rotary member including a working portion including an edge portion which is rotated around a central axis equal to or substantially parallel with the longitudinal axis, the rotary member capable of moving the edge portion from the first holding portion to the second holding portion； a first guide portion provided in the first holding portion and capable of guiding the edge portion toward the second holding portion through the holding surface of the first holding portion； and a second guide portion provided in the second holding portion, and capable of guiding the edge portion to the second holding portion through the holding surface of the first holding portion.
