To provide a breaker which dispenses with a replacement component even during an operating stoppage due to overload and can cut time required for the resumption of a breaking work.

This breaker comprises (1) a crank slider mechanism 60 which can change the rotary motion of a crank 65 pivoted at a rotating shaft 65 to the straight-line motion of a slider 68, (2) a stopper 61 which limits the rotation range of the crank 66 to one side, (3) a spring 62 which urges the slider 68 so as to allow the crank 66 to be pressed against the stopper 61, and (4) a retaining member 40 which effects the resistance to the urging force of the spring 62 by transferring a breaking reaction acting on an anvil 34 to the crank 66. In addition, the slider 68 reaches the upper dead spot due to the breaking reaction resisting the urging force of the spring 62, and the crank 66 changes its rotating direction to a direction in which the crank 66 becomes remote from the stopper 61 under the urging force received from the spring 62. Thus, the anvil 34 retreats from a breaking chamber 27.