Described is a drive device with applications in particular in mobile excavators, wheeled loaders and similar plant, which comprises a power-shift planetary gearbox (4) driven by a hydraulic motor (3). The gearbox (4) preferably has two gears which can be alternately engaged and disengaged hydraulically by means of friction clutches (12, 13). The two clutches (12, 13) are spring-loaded and controlled by oil pressure generated by an oil pump (21) and supplied to both clutches (12, 13) via a gear-shift valve (23). One of the clutches (13) is designed as a brake and has a static leakage-oil-free oil supply. When the pressure generated by the oil pump (21) sinks below a given value, the gear-shift valve (23) is switched into its 2nd-gear position in which only the brake is acted on by the oil pressure. In an emergency in which only a limited amount of hydraulic oil is available, this device makes it possible for the machine to continue operating for a certain length of time since only one almost leakage-oil-free clutch is acted on by the hydraulic oil.