To prevent the fuel pressure regulating diaphragm of a constant fuel chamber from being applied with a high negative pressure and being unreasonably deformed to cause functional reduction and early deterioration when a starting pump is operated.

An air passage 36 sucking air into the starting pump chamber 35 of a manual starting pump 33 is branched from a fuel passage 15 to a constant fuel chamber 16 from a fuel pump 5, a fuel valve 22 is kept closed when the starting pump 33 is operated, and the starting fuel is retained in the fuel passage 15. The check valve 37 of the air passage 36 is fixed at the closed position by the engine intake negative pressure for a normal fuel feed.