PURPOSE: To obtain the artificial leg by which a user can walk without a sense of imcompatibility by forming a throttle between a valve body and a passage, determining a position of the valve body by a difference between air pressure of a pressure chamber applied to one end of the valve body and air pressure of the outside applied to the other end and spring force of a spring resisting the pressure difference and adjusting an opening degree of the throttle.

CONSTITUTION: When a piston 7 moves to a head cover 4 side at the time of bending the high part and the leg part, air pressure of a head side chamber 8 rises, air pressure of a rod side chamber 9 falls and a difference is generated in the air pressure, and a back pressure chamber 20 communicating with the head side chamber 8 by a connecting passage 22 becomes the same pressure as the air pressure of the head side chamber 8 because air flows in. By a difference of the air pressure applied to the upper face and the lower face of a valve body 16, the valve body 16 moves to the head cover 4 side against spring force of a tension spring 17. As a result, an opening degree of a throttle 20 formed by a conical side periphery of the valve body 16 and a small diameter hole 20 is decreased, the quantity of air which flows out to the rod side chamber 9 from the head side chamber 8 is limited, and a cylinder 1 displays a control action of the thigh part and the leg part.