Ultrasonic treatment tool for joints and ultrasonic treatment system for joints

An ultrasonic treatment tool for joints that has: a treatment part that treats a subject by means of ultrasonic vibrations; a first vibration element that generates first ultrasonic vibrations that have a first frequency; a second vibration element that generates ultrasonic vibrations in a first mode that generates the first ultrasonic vibrations or in a second mode that generates second ultrasonic vibrations that have the first frequency and an arbitrary phase difference relative to the first mode; and a vibration transmission part that transmits, to the treatment part, third ultrasonic vibrations obtained by synthesizing the first ultrasonic vibrations generated by the first vibration element and the first ultrasonic vibrations or the second ultrasonic vibrations generated by the second vibration element.