A prosthetic knee joint includes a knee portion coupled to the socket, a cylinder that is coupled to the knee portion and limits or aids operation of the knee portion, a knee angle sensor that directly or indirectly detects a knee angle value, and a control unit that controls driving of the cylinder. The control unit may calculate a knee angular velocity value based on the knee angle value detected by the knee angle sensor. The control unit determines whether the knee portion is in a knee still state based on the knee angular velocity value and automatically restricts contraction of the cylinder based on a time duration in which the knee portion is in the knee still state.
