To provide a percussion hammer that can dissolve the defect of an initial system.

The motion of a percussion hammer 1 is controlled by a main valve 3, and this control motion is controlled by another control valve 9. When pressure acting upon the control valve 9 rises to the specified valve, the main valve 3 changes its state. A liquid-operated percussion hammer of such constitution has a control device 21 fitted to a return duct 13, and the outflow of a pressurized fluid from the percussion hammer is adjusted by means of the control device 21. The charging speed of an accumulator 7, that is, the distance of return motion of a percussion piston 1, is proportional to flow resistance imparted by the control device 21.