A surgical treatment of a ligament of a knee joint under an arthroscope, includes: forming concave holes from the region of the tibia to which the ligament adheres toward an inner side of a rough surface of the tibia and from the region of the femur to which the ligament adheres toward an outer surface of a lateral condyle of the femur by ultrasonically vibrating the treating portion； forming tunnels between the concave hole of the tibia and the medial side of the rough surface of the tibia using the concave hole of the tibia and between the concave hole of the femur and the lateral surface of the lateral condyle of the femur using the concave hole of the femur.
