A surgical instrument can grasp a living tissue (S) by first and second grasping members (25, 59), can cut the grasped tissue by ultrasonic vibration from a grasping surface (61) of an ultrasonic vibrating portion (31) in the second member, and can coagulate the cut portion of the tissue by high-frequency current between first and second electrode portions in the first and second members. A pressing portion (55) is provided in the first member to be in contact with the grasped tissue and presses the tissue in cooperation with the grasping surface of the vibrating portion. Each of the first and second electrode portions includes electrodes in both sides of the pressing portion. The electrodes of the first and second electrode portions cooperate to press the grasped tissue while the tissue is pressed by the pressing portion of the first member and the grasping surface of the vibrating portion.
