To enable the effective and simple monitoring for securing the accurate taking-out of a mold by providing one piece of an exhaust air introducing pipe or an exhaust air storage disposing a pressure monitoring gage therein in a hammer unit.

Compressed air is fed to a compressed air supplying pipe 5 and then, the hammer head 7 develops a striking movement and the exhaust air is exhausted through an exhaust air conduit 6. The pressure monitoring gage 9 is disposed with some distance from the hammer unit 4 and further, from an opening end part 8 and connected with an electronic assessment circuit through an electric connecting cables 10. The compressed oil vigorously pulsates at the time of exhausting from the hammer unit 4, but since the exhaust air conduit 6 is long, the pulsation is weakened at the tip part. Since the pressure monitoring gage 9 is disposed with the sufficient distance from the opening end part 8, the pulsation can sufficiently be detected even at the opening end 8. In the case that the hammer head does not contact with a casting, the pulsation can be detected with the increase of working frequency.