In a hydropneumatic accumulator, the gas volume contained therein is monitored by measuring the volume increase in the hydraulic fluid, which takes place during a pressure increase at a given minimum pressure. Moreover, for monitoring purposes, the hydraulic pressure is measured and a signal transmitted at insufficient gas volume as a function of the volume increase and the pressure increase. In order to obtain reliable signals concerning the filling state of the accumulator at all ambient operating temperatures, the temperature of the environment and the gas volume is detected, a standard value for the volume increase proportional to the ratio of the gas temperature to the minimum pressure determined and the volume increase causing the pressure increase compared to this standard value.