A surgical treatment of an ACL or a PCL of a knee joint under an arthroscope, includes: contacting a treating portion of an ultrasonic device with a start region to which the ACL or the PCL of a femur adheres, and excising the femur and a remaining ligament of the ACL, or the femur and a remaining ligament of the PCL by ultrasonically vibrating the treating portion, thereby exposing a footprint of the femur; and contacting the treating portion with an end region to which the ACL or the PCL of a tibia adheres, and excising the tibia and a remaining ligament of the ACL, or the tibia and a remaining ligament of the PCL by ultrasonically vibrating the treating portion, thereby exposing a footprint of the tibia.