A two-joint arm mechanism equipped with a bi-articular driving means is disclosed which is capable of controlling position, force and stiffness on a loading point at the forward end of a second arm independently, precisely and readily. The two-joint arm mechanism equipped with a bi-articular driving means comprises: a first arm (1) pivoted at its rear end on a base (3) as a foundation, a second arm (5) pivoted at its rear end (5a) on the forward end of the first arm, and a loading member (8) mounted on the forward end (5b) of the second arm; wherein two driving means (9,10) are respectively connected to the first arm and the second arm for independently exerting rotational forces on the respective arms in order to independently rotate the first arm and the second arm on pivot pins thereof to cause extension movement or flexion movement of the arm mechanism, a single driving means (11) capable of acting simultaneously on both the arms is connectively mounted between the base and the second arm, and by simultaneously actuating these driving means, both the arms are rotated to move the loading point at the forward end of the second arm forward or backward relative to the base to effect positioning of the loading point at the forward end of the second arm.
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