In this paper, an assistance method that controls the joint stiffness and antagonized angle using variable elastic elements is proposed. The proposed system changes the joint stiffness and antagonized angle so that they correspond to the phase of movement, and performs movement assistance in cooperation with the wearer. As a structurally variable configuration of stiffness and antagonized angle, a joint structure in which an artificial muscle and tension spring are antagonistically arranged is proposed. A mathematical model of one side spring antagonized joint is proposed and its characteristics is examined.