To provide a substantial safety device informing that a driving device has reached a critical accumulated number of uses.

A fixing part laid on the top face of a column or the upper face of a girder is installed at the upper end of a guide bar 1 and a driving weight is provided at the lower part of the guide bar 1 to freely slide vertically along the guide bar 1. And further, a support stopper 6 supporting the driving weight and serving as the lower limit of the sliding, is provided at the tower part of the guide bar. A fitting hole 7 is formed in the guide bar and an erection bar 8 is inserted in the fitting hole 7 and laid therein in the direction crossing at nearly right angles against the longitudinal direction of the guide bar and the support stopper 6 is attached to the erection bar 8 and fixed to the guide bar 1. The second fitting hole 9 is formed almost right under the fitting hole 7 and at a position separated by a specified distance from the fitting hole 7. The erection bar 8 can be transferred from the fitting hole 7 to the second fitting hole 9 with cracks caused by deformation, expansion, or metal fatigue of the fitting hole 7 by repeated impulses of a number of sliding falls of the driving weight.