An apparatus for controlling the ratio of air to fuel quantity of the operational mixture to be introduced into the combustion chambers of an internal combustion engine which includes an air flow rate meter moving under differential pressure against a constant hydraulic restoring force, which air flow rate meter adjusts a metering cross section in a supply line leading to a fuel injection pump, with the pressure drop at the metering cross section being maintained constant with the aid of a differential pressure valve. The air flow rate meter is part of a known apparatus which controls the fuel component in accordance with the quantity of aspirated air and also controls the component of exhaust gas to be fed back. The hydraulic restoring pressure for the air flow rate meter is drawn via a throttle from the supply side of a supply pump which supplies the injection pump with fuel under an rpm-dependent pressure and with a quantity of fuel intended for flushing and the pressure downstream of the throttle is maintained at a constant value by means of a pressure maintenance valve. The working chambers of the injection pump communicate only with either the injection lines or the fuel supply line controlled by the air flow rate meter, so that the control result is not adulterated by the flushing quantity or by a shutoff quantity. In this manner, the injection pump and the control device can be supplied with fuel and with pressure fluid by means of a single supply pump.