A pneumatic tool includes a body having a pressure accumulation chamber formed therein for accumulating compressed air. A cap are mounted on the body and has a cap chamber formed therein for communication with the pressure accumulation chamber. The cap has a joint for connection with an air hose from a compressed air source. A gasket is interposed between the pressure accumulation chamber and the cap chamber from each other. The gasket itself forms a valve for preventing a counterflow of the air from the pressure accumulation chamber to the cap chamber, so that exhaust sounds of the air is prevented from being produced when the air hose is disconnected from the joint.