PURPOSE: To adjust the injection amount of fuel according to the change of atmospheric pressure in the inside of a fuel injection pump.

CONSTITUTION: The fuel injection pump 1 of a diesel engine is provided with a pressure governing chamber 20 connected to a pump chamber 16 through an orifice 32; end a pressure governing valve 21 to conduct the pressure change of the oil pressure of the pressure governing chamber 20 according to the change of atmospheric pressure. Bellows 55 to carry out extending/contracting deformation by means of the oil pressure in the pressure governing chamber 20 are provided in the pressure governing chamber 20. In B cylinder chamber 19, a pressure leading chamber 23 and an atmospheric pressure chamber 24 opened to atmosphere through B fuel tank 5 are dividingly formed with a piston 22 to which a push rod 18 is connected, interposed. An inflow valve 35 connected to the bellows 33 is provided between the pressure governing chamber 20 and the pressure leading chamber 23, end the chamber 20 and the chamber 23 are connected to each other, end a fuel injection amount is adjusted by an oil pressure difference between the atmospheric pressure chamber 24 and the pressure leading chamber 23 that is generated by the opening of the inflow valve 35.