A treatment device configured to hold a living tissue includes a swing member supported by a first grasping member and rotatable in a first direction and in an opposite direction opposite to the first direction. The swing member includes a distal end close to a distal end portion of the first grasping member and a proximal end close to the proximal end portion of the first grasping member, and a support shaft thereof is supported on a side close to the distal end including a middle position between the distal end and the proximal end. A first holding surface is provided on the swing member close to a side of the second grasping member and grasps the living tissue. A second holding surface is provided on the second grasping member close to a side of the swing member and which faces the first holding surface and which is configured to hold the living tissue together with the first holding surface of the swing member.
