A treatment system includes an energy source, a pair of holding portions, an output portion and a cooling section. To hold a living tissue of a treatment target, at least one of the pair of the holding portions relatively moves with respect to the other holding portion. The output portion is disposed on at least one of the holding portions and connected with the energy source. Moreover, the output portion thermally denatures the living tissue, when the energy is supplied from the energy source. The cooling section inhibits the thermal spread in a direction away from the output portion.