A treatment device to treat a living tissue, includes: first and second holding portions including a longitudinal axis and including respective holding surfaces opening and closing in an opening/closing direction orthogonal to or substantially orthogonal to the longitudinal axis and capable of holding the living tissue therebetween a rotary member including a working portion including an edge portion capable of cutting the living tissue by being 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, the second guide portion capable of cutting the living tissue in guiding the edge portion to the second holding portion through the holding surface of the first holding portion.
