A hydraulic hammering device comprising: a cylinder; a piston configured to be slidably fitted into the cylinder in such a manner as to be capable of advancing and retracting; a first control valve configured to control advancing and retracting movements of the piston; an auto-stroke mechanism configured to switch a piston stroke of the piston between a regular stroke and a short stroke shorter than the regular stroke; an idle strike prevention mechanism configured to decompress an inside of a circuit configured to hydraulically drive the piston to lower than a working pressure; and characterized by a second control valve configured to select either mode of the auto-stroke mechanism and the idle strike prevention mechanism, wherein, to the second control valve, a shared spool including an auto-stroke setting portion and an idle strike prevention setting portion at the same time is slidably fitted, and a mode selection means for allowing and cutting off both of supply of pressurized oil to the auto-stroke setting portion and discharge of pressurized oil from the idle strike prevention setting portion is disposed, and the mode selection means is configured in such a way that: when, while allowing pressurized oil to be supplied to the auto-stroke setting portion, prohibiting pressurized oil from being discharged from the idle strike prevention setting portion, the auto-stroke mechanism is selected, and when, while prohibiting pressurized oil from being supplied to the auto-stroke setting portion, allowing pressurized oil to be discharged from the idle strike prevention setting portion, the idle strike prevention mechanism is selected. a cylinder; a piston configured to be slidably fitted into the cylinder in such a manner as to be capable of advancing and retracting; a first control valve configured to control advancing and retracting movements of the piston; an auto-stroke mechanism configured to switch a piston stroke of the piston between a regular stroke and a short stroke shorter than the regular stroke; an idle strike prevention mechanism configured to decompress an inside of a circuit configured to hydraulically drive the piston to lower than a working pressure; and characterized by a second control valve configured to select either mode of the auto-stroke mechanism and the idle strike prevention mechanism, wherein, to the second control valve, a shared spool including an auto-stroke setting portion and an idle strike prevention setting portion at the same time is slidably fitted, and a mode selection means for allowing and cutting off both of supply of pressurized oil to the auto-stroke setting portion and discharge of pressurized oil from the idle strike prevention setting portion is disposed, and the mode selection means is configured in such a way that: when, while allowing pressurized oil to be supplied to the auto-stroke setting portion, prohibiting pressurized oil from being discharged from the idle strike prevention setting portion, the auto-stroke mechanism is selected, and when, while prohibiting pressurized oil from being supplied to the auto-stroke setting portion, allowing pressurized oil to be discharged from the idle strike prevention setting portion, the idle strike prevention mechanism is selected. when, while allowing pressurized oil to be supplied to the auto-stroke setting portion, prohibiting pressurized oil from being discharged from the idle strike prevention setting portion, the auto-stroke mechanism is selected, and when, while prohibiting pressurized oil from being supplied to the auto-stroke setting portion, allowing pressurized oil to be discharged from the idle strike prevention setting portion, the idle strike prevention mechanism is selected.