This paper deals with mechanical stiffness control of multi-DOF joint. It fundamentally mimics the skeleto-muscular system of human articulation, in which at least two muscles cooperatively handle one DOF under their antagonistic action. In the first part of the paper one describes a novel actuator called ANLES (actuator with non-linear elastic system) that mimics a skeletal muscle in the sense of having a non-linear elasticity. Next one introduces a basic formula for controlling stiffness of the joint as well as its angles using multiple ANLESes. A new mechanism for the wrist joint having three DOF is proposed on the practical feasibility base, in which only four ANLESes with one additional DC-motor are used to control the stiffness of the three DOF wrist. It follows the simulation analysis for evaluating the controllability of the stiffness. It also shows the one DOF wrist joint controlled by two ANLESes