A fuel feeder of an engine, comprising a gas-liquid separating device separating oil mist produced in an engine case from air by a labyrinth. An automatic fuel valve is operated by the pressure pulsation of the air from which the oil mist is separated by the gas-liquid separating device. Accordingly, the automatic fuel valve can be prevented from being improperly operated due to the stagnation ofoil therein by minimizing the entry of the oil mist into the automatic fuel valve. Furthermore, a breather passage for feeding the air from which the oil mist is separated by the gas-liquid separating device to a breather device is allowed to communicate with the automatic fuel valve through a negative pressure tube. As a result, a special passage for transmitting the pressure pulsation of the air in the engine case to the automatic fuel valve must not be installed in the fuel feeder.