To provide a hydraulic breaker by which the striking sound of a piston 12 is reduced to leak to the outside sharply.

The hydraulic breaker is provided with a cylinder 10, a striking piston 12 contained retractably within the cylinder 10, a hydraulic actuating means formed between the outer peripheral portion of the piston 12 and the inner peripheral portion of the cylinder 10 and used for reciprocating the piston 12, and a chisel 11 retained within the cylinder 10 and struck by the piston 12. A supporting member 13 for supporting a striking load directly by the piston 12 is arranged such that it is usually isolated from the end face of the piston 12 and abutted against the end face of the chisel 11 between the piston 12 and the chisel 11 within the cylinder 10, in this hydraulic breaker. An airtight space 25 is provided between the piston 12 and the supporting member 13.