A device (1) simulates the recoil of a firearm and has a breechblock (60) with a knockover slide (63). To avoid freezing up and outward emissions, a control mechanism controls a hydraulic working piston in working connection with the breechblock (60). A valve pressure lever (11) is deflected by movement of the knockover slide (63) to open a pressure valve (20), as a result of which fluid is fed to the working piston. The valve (20) has a movable separating piston (14) separating a hydraulic chamber (13) tightly from a gas chamber (17) filled with compressed gas. The separating piston (14) is acted on by the compressed gas. The working piston at the end of an adjusting movement brings about the closing of the valve (20) and opening of a discharge valve. The hydraulic fluid is guided, with open discharge valve, from the working piston into a return chamber (24).