PURPOSE: To prevent the occurrence of cavitation and erosion, and improve fuel charging efficiency by providing a negative pressure prevention passage with a nonreturn valve allowing only a fuel flow from a main fuel passage to a pressure chamber.

CONSTITUTION: During engine operation, a plunger 16 in a pump element 10 rises and after the upper edge of the plunger 16 passes the upper end of a feed hole 24, fuel in a pressure chamber 20 is pressurized and a delivery valve 18 is thereby opened to feed fuel to a fuel injection nozzle 36 under pressure. In this case, a check valve 46 is close. Then, the plunger 16 enters downward stroke, and is displaced to a position slightly lower than the upper dead center, thereby temporarily interrupting communication between the chamber 20 and a fuel chamber 22. Consequently, when negative pressure tends to be generated in the pressure chamber 20, the force of a weak spring 50 is overcome by differential pressure between fuel pressure in a main fuel passage and fuel pressure in the chamber 20 to open the check valve 46. As a result, fuel is fed to the chamber 20 from an oil gallery 26 and the occurrence of large negative pressure is properly prevented.