A treatment instrument (12) applies energy to a living tissue to treat the living tissue (LT). The treatment instrument includes a sealing member (76, 86) and a maintaining member (78, 88). The sealing member joins desired sealed regions of at least two living tissues when the energy is applied to the desired sealed regions in a state where the desired regions of the at least two living tissues are sealed. The maintaining member is provided independently from the sealing member and maintains living tissues near the sealed region in a contact state when energy is applied separately from the sealing member in a state where the tissues near the region sealed by the sealing member are in contact with each other.
