A hydraulic hammering device enables an auto-stroke mode and an idle strike prevention mode to coexist with a simple circuit configuration. The device includes a first control valve to control advancing and retracting movements of a piston, an auto-stroke mode and an idle strike prevention mode, and a second control valve to select either of the auto-stroke mode or the idle strike prevention mode. To the second control valve, a shared spool is slidably fitted and a mode selection means is disposed. When the mode selection means allows supply of pressurized oil to an auto-stroke setting portion of the shared spool and prohibits discharge of pressurized oil from an idle strike prevention setting portion, the auto-stroke mode is selected. When prohibiting supply of pressurized oil to the auto-stroke setting portion and allowing discharge of pressurized oil from the idle strike prevention setting portion, the idle strike prevention mode is selected.