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.