An ultrasonic surgical instrument includes an ultrasonic vibrator, a vibration transmission section, a grip member, a pad member provided at a position of the grip member which faces the treatment section, and a planar facing surface disposed on the pad member. A distal end portion of the treatment section faces the pad member, and is curved from a proximal end portion side of the treatment section toward the distal end portion side of the treatment section in a direction away from the facing surface. The pad member includes a protruding portion which is disposed on the facing surface, protrudes from the facing surface toward the distal end portion of the treatment section, and abuts on the distal end portion of the treatment section while the grip member is closed.
