Abstract: A hydraulic breaker includes a piston which is designed in the five-staged configuration including a first stage, a second stage, a third stage, a fourth stage and a fifth stage. The second stage is dimensioned to have a largest diameter, the fourth stage is dimensioned to have a larger diameter and the first stage, the third stage and the fifth stage are dimensioned to a same smallest diameter, respectively. A piston reversing chamber, a low pressure hydraulic chamber in which low pressure is normally present for the piston, a low speed pilot chamber for driving the piston at a low speed, a high speed pilot chamber for driving the piston at a high speed and a high pressure hydraulic chamber in which high pressure is normally present for the piston are sequentially formed in the space between the piston and the inner wall surface of a cylinder.