An air pressure circuit comprising a compressor (3) cylinder which is divided into two chambers by a slidable piston, a suction (1) port and an exhaust port (2), each having a valve and mounted on one chamber of the cylinder, inhaling air of a pressure higher than that of atmospheric air from the suction port and exhausting the piston-compressed air from the exhaust port. The air pressure in the side of suction port is introduced to the other chamber (3a) of the cylinder.