PURPOSE: To prevent the dislocation of a cylinder fitted to an arm movable into an optional position by absorbing reaction generated by the movement of a piston.

CONSTITUTION: A nonreaction cylinder has a cylinder 1 fitted to an arm movable into an optional position and having a compressed gas lead-in port 7b, a piston 4 provided in the cylinder 1 and moved in one direction by the pressure of the led-in compressed gas, a driven member 6 moved along with the piston 4 so as to collide with a target, and a counter weight piston 8 provided in the cylinder 1 and moved in the reverse direction to the moving direction of the piston 4 by the pressure of the led-in compressed gas so as to offset reaction generated by the movement of the piston 4.