A device (10, 50, 60) for controlling the pressure of a fluid in a two-phase fluid loop with mechanical pumping, the two-phase fluid loop with mechanical pumping comprising: - a closed circuit, through which a heat transfer fluid flows; - at least one evaporator comprising an inlet and an outlet, through which the fluid flows from the inlet of the evaporator in liquid form (20-liq) towards the outlet of the evaporator, the evaporator being configured to transform the fluid in liquid form (20-liq) into fluid in partially gaseous form (20-g); - at least one condenser comprising an inlet and an outlet, through which the fluid in partially gaseous form (20-g) flows from the inlet of the condenser towards the outlet of the condenser, the condenser being configured to transform the fluid in partially gaseous form (20-g) into fluid in liquid form (20-liq); - a pump, disposed between the outlet of the condenser and the inlet of the evaporator, intended to move the fluid in the closed circuit from the evaporator towards the condenser in partially gaseous form (20-g) and from the condenser towards the evaporator in liquid form (20-liq); - a fluid reservoir connected to the closed circuit, intended to compensate for the variations in the volume of fluid in the closed circuit; the control device comprising: - a device for measuring the temperature of the fluid in liquid form (20-liq) able to provide a measured value of the temperature of the fluid in liquid form; - a device for measuring the pressure of the fluid at a point of the closed circuit able to provide a measured value of the pressure of the fluid; - a device for adjusting the pressure in the closed circuit; - a means for controlling the device for adjusting the pressure, or the saturation temperature, as a function of the measured value (24, 29) of the pressure of the fluid, or of the saturation temperature, and of a setpoint value (Pcons, Tcons) of the pressure, or of the saturation temperature, characterised in that said setpoint value of the pressure (Pcons), or of the saturation temperature (Tcons), is variable according to the measured value of the temperature of the fluid in liquid form (20-liq) and of a maximum value of the temperature of the reservoir or of a maximum pressure in the closed circuit over a previously defined period. - a closed circuit, through which a heat transfer fluid flows; - at least one evaporator comprising an inlet and an outlet, through which the fluid flows from the inlet of the evaporator in liquid form (20-liq) towards the outlet of the evaporator, the evaporator being configured to transform the fluid in liquid form (20-liq) into fluid in partially gaseous form (20-g); - at least one condenser comprising an inlet and an outlet, through which the fluid in partially gaseous form (20-g) flows from the inlet of the condenser towards the outlet of the condenser, the condenser being configured to transform the fluid in partially gaseous form (20-g) into fluid in liquid form (20-liq); - a pump, disposed between the outlet of the condenser and the inlet of the evaporator, intended to move the fluid in the closed circuit from the evaporator towards the condenser in partially gaseous form (20-g) and from the condenser towards the evaporator in liquid form (20-liq); - a fluid reservoir connected to the closed circuit, intended to compensate for the variations in the volume of fluid in the closed circuit; - a device for measuring the temperature of the fluid in liquid form (20-liq) able to provide a measured value of the temperature of the fluid in liquid form; - a device for measuring the pressure of the fluid at a point of the closed circuit able to provide a measured value of the pressure of the fluid; - a device for adjusting the pressure in the closed circuit; - a means for controlling the device for adjusting the pressure, or the saturation temperature, as a function of the measured value (24, 29) of the pressure of the fluid, or of the saturation temperature, and of a setpoint value (Pcons, Tcons) of the pressure, or of the saturation temperature, characterised in that said setpoint value of the pressure (Pcons), or of the saturation temperature (Tcons), is variable according to the measured value of the temperature of the fluid in liquid form (20-liq) and of a maximum value of the temperature of the reservoir or of a maximum pressure in the closed circuit over a previously defined period.