An internal combustion engine driven by a gaseous fuel, with quantity regulation in a lower load range and quality regulation in an upper load range. A gas pressure regulator is provided for controlling a gas flow to an air-gas mixer, with a throttle valve actuatable by an accelerator pedal being arranged in an intake line downstream of the air-gas mixer, whereby the gas pressure regulator is movable in a closing direction through a control line, by a diaphragm by vacuum prevailing in the intake line in a vicinity of the throttle valve. A control valve, influenced by the accelerator in the quality control range, is disposed in a control line. The control line branches off the intake line upstream of the throttle valve or off the air-gas mixer. A throughput or through-flow cross section in the control valve decreases with increasing loads in a direct relationship to a position of the accelerator until the control valve closes at full load. The control line between the control valve and gas pressure regulator is connected to outside air through a fixed throttle.