An ultrasonic treatment system for a joint has an ultrasonic transducer configured to generate ultrasonic vibration at a predetermined frequency, a treatment unit configured to treat a bone or a cartilage with the ultrasonic vibration, a frequency measurement unit configured to measure the frequency of the ultrasonic vibration of the treatment unit, a calculation unit configured to calculate a tilt indicating change, in a predetermined time, of the frequency measured with the frequency measurement unit, and a controller configured to determine whether change of absolute value of the tilt is equal to or larger than predetermined absolute value of the tilt.