An ultrasonic surgical instrument (21) includes an ultrasonic vibrator (28) configured to generate ultrasonic vibration, a vibration transmission section (29) configured to transmit the ultrasonic vibration generated in the ultrasonic vibrator (28), a treatment section (32) formed in a distal end portion of the vibration transmission section (29), and configured to transmit the ultrasonic vibration from the ultrasonic vibrator (28) to living tissue, a grip member (33) openably or closably provided relative to the treatment section (32) and a pad member (49) provided at a position of the grip member (33) which faces the treatment section (32), and configured to abut on the treatment section (32) while the grip member (33) is closed. A distal end portion of the pad member (49) includes a protruding portion (60) which protrudes toward the treatment section (32) on a side facing the treatment section (32).
