There is provided an air-cylinder apparatus for use in a prosthetic limb capable of effectively adjusting the pressure characteristics over a wide range of walking speed. A second chamber 82 defined by a piston 113 is increased in pressure by air confined therein in accordance with the bending motion of the knee. Air is restricted from flowing out of the second chamber 82 by a constant throttle valve 140. In addition, the second chamber 82 is divided into plural chambers 821, 822 in accordance with increase in bending angle of the knee and air is restricted from flowing out of the newly divided chambers 821,822 by throttle valves corresponding thereto. The division of the second chamber 82 is achieved by mutual engagement between a projection 1140b on the piston side and a recess 1127 on the bottom part of a cylinder body.
