To provide a hydraulic hammer capable of automatically changing an impact stroke, and capable of efficiently and precisely controlling the stroke.

This hydraulic hammer 1 impacts a chisel 3 by reciprocating an impact piston 2; and has a brake chamber 13 becoming a room sealed by the impact piston 2, when the impact piston 2 moves by a specific distance in the impact direction of the chisel 3, by going over a normal impact position, a stroke control valve 29 for issuing a signal, so as to reduce impact force, by shortening the stroke, when pressure of the brake chamber 13 exceeds a prescribed value, and a holding mechanism for holding the stroke control valve 29 for a prescribed time in its switching position; and has a supply mechanism for supplying a hydraulic fluid to the brake chamber 13, so that the impact piston is made to escape from the brake chamber 13, when the impact piston 2 enters the brake chamber 13 in starting.