To make quick mass transfer possible with a simplified construction.

A machine tool 1 contains a device 3 operatable by a piston cylinder unit 10 and the unit 10 contains a medium operating type piston 12 practicing a stroke 15 limited by an end stopper, while the piston 12 is in combination with a driven member 13 for transmitting the stroke 15 to an operated device 3. An attenuation device is provided and the piston motion is attenuated when the attenuation device increases the back pressure, which is for suitably reducing the speed of the transferring piston 12, and the piston approaches at least one of the end stopper.