A treatment instrument includes: a sheath; and an end effector that is provided at a distal end of the sheath. The end effector is capable of gripping a living tissue and applying high frequency energy to the living tissue. The end effector includes a treatment surface, and a pair of electrodes that can grip the living tissue and apply the high frequency energy to the living tissue. The treatment surface includes a distal end area that is provided on a distal end side of the treatment surface, and another area that is provided on a proximal end side of the treatment surface. The distal end area applies, to the living tissue, high frequency energy that is higher than high frequency energy applied by the other area. One of the pair of electrodes includes a distal end portion and a proximal end portion.