A ultrasonic treatment apparatus includes a handpiece. The handpiece includes a probe and a hollow sheath. The sheath covers and protects the probe. The probe has a rod-shaped main body portion and a treatment portion provided at the distal end of the main body portion. The treatment part includes a cutting region. The sheath includes a first portion covering the main body portion and a second portion covering the curved portion of the treatment portion. The physician inserts the probe and sheath into the joint space and strikes the cutting area against the bone. When ultrasonic vibration is transmitted to the probe, the bone is cut.
