A work machine comprising: a machine body; a work equipment mounted on the machine body; a hydraulic breaker attached to a distal end of the work equipment; a control valve (33, 34) adapted to control hydraulic oil fed to the hydraulic breaker; a single rod type hydraulic cylinder adapted to operate the work equipment downward so that the hydraulic breaker is pressed against an object to be crushed; and an operation unit adapted to operate the hydraulic cylinder in a contracting direction so that the work equipment is operated downward; characterised in that the work machine further comprises: pressure sensors (44, 45) respectively adapted to detect pressure at the head side and pressure at the rod side of the hydraulic cylinder; a changeover switch (25, 26, 27, 28) that is capable of switching the hydraulic breaker between an automatic hammering inhibiting mode, in which operation of the hydraulic breaker is inhibited, and an automatic hammering authorizing mode, in which operation of the hydraulic breaker is permitted; and a controller having a function of controlling the control valve (33, 34) of the hydraulic breaker so that the control valve (33, 34) opens only when pressure at the head side and pressure at the rod side of the hydraulic cylinder respectively detected by the pressure sensors, are in a given range of pressing force, while the hydraulic breaker is in the automatic hammering authorizing mode as a result of switching operation of the changeover switch (25, 26, 27, 28). a machine body; a work equipment mounted on the machine body; a hydraulic breaker attached to a distal end of the work equipment; a control valve (33, 34) adapted to control hydraulic oil fed to the hydraulic breaker; a single rod type hydraulic cylinder adapted to operate the work equipment downward so that the hydraulic breaker is pressed against an object to be crushed; and an operation unit adapted to operate the hydraulic cylinder in a contracting direction so that the work equipment is operated downward; characterised in that the work machine further comprises: pressure sensors (44, 45) respectively adapted to detect pressure at the head side and pressure at the rod side of the hydraulic cylinder; a changeover switch (25, 26, 27, 28) that is capable of switching the hydraulic breaker between an automatic hammering inhibiting mode, in which operation of the hydraulic breaker is inhibited, and an automatic hammering authorizing mode, in which operation of the hydraulic breaker is permitted; and a controller having a function of controlling the control valve (33, 34) of the hydraulic breaker so that the control valve (33, 34) opens only when pressure at the head side and pressure at the rod side of the hydraulic cylinder respectively detected by the pressure sensors, are in a given range of pressing force, while the hydraulic breaker is in the automatic hammering authorizing mode as a result of switching operation of the changeover switch (25, 26, 27, 28). pressure sensors (44, 45) respectively adapted to detect pressure at the head side and pressure at the rod side of the hydraulic cylinder; a changeover switch (25, 26, 27, 28) that is capable of switching the hydraulic breaker between an automatic hammering inhibiting mode, in which operation of the hydraulic breaker is inhibited, and an automatic hammering authorizing mode, in which operation of the hydraulic breaker is permitted; and a controller having a function of controlling the control valve (33, 34) of the hydraulic breaker so that the control valve (33, 34) opens only when pressure at the head side and pressure at the rod side of the hydraulic cylinder respectively detected by the pressure sensors, are in a given range of pressing force, while the hydraulic breaker is in the automatic hammering authorizing mode as a result of switching operation of the changeover switch (25, 26, 27, 28).