To provide a fuel injection pump capable of raising fuel injection pressure in a low load operating range while suppressing significant rise in the fuel injection pressure in a high load operating range.

In this fuel injection pump, a fuel is introduced and forcibly fed to a pressurizing chamber from a fuel reservoir chamber along with reciprocation of a plunger. A lead section is provided with a vertical fuel passage formed along the axial direction of the plunger and an inclined edge section with a fuel forced-feeding ending position varied according to the rack position of the plunger, which is communicated with the vertical fuel passage and inclined relative to the axial direction of the plunger. The plunger is provided with a pressure relief passage with at least a part of its passage area smaller than that of the lead section. The pressure relief passage allows the pressurizing chamber and an intake/exhaust port to be communicated at the rack position in the high load operating range.