An ultrasonic treatment instrument for articulations has a bone abrasion mode in which vibration is performed at a first frequency and a first amplitude, and a cartilage dissolution mode in which vibration is performed at a second frequency which is higher than the first frequency, and a second amplitude which is less than the first amplitude, wherein a first vibration velocity, which is a product of the first frequency and the first amplitude, and a second vibration velocity, which is a product of the second frequency and the second amplitude, coincide or substantially coincide.