A pressure generator, wherein a piston (13) is stored in a cylinder (10) reciprocatingly in axial direction, a piston rod (14) fixed to the piston (13) is projected to the outside through a rod cover (12), check valves (31, 32) for negative pressure allowing air to flow into expansion and contraction chambers (21, 22) and stopping air to flow in reverse direction are installed in negative pressure feed passages (23, 24) connected between the expansion and contraction chambers (21, 22) and operating ports (5, 6), check valves (33, 34) for exhaust gas allowing air to flow from the expansion and contraction chambers (21, 22) to the outside and stopping air to flow in reverse direction are installed in exhaust gas flow passages (25, 26) for communicating the expansion and contraction chambers (21, 22) with the outside, and the negative pressure feed passages (23, 24) are brought into a vacuum state by the reciprocating motion of the piston (13).
