PURPOSE: To lower the cost in comparison with that required for an electronic pressure-increasing means and enhance the reliability of the device by providing a pressure-increasing apparatus between a fuel injection pump and an injection nozzle and thereby enabling high-pressure injection mechanically.

CONSTITUTION: The main body 1 of the pump has a plunger 3 which is made to perform reciprocating motions by a cam 2. Into the upper pressure chamber 4 and intermediate circular groove 3a of the plunger 3 is introduced fuel through ports 11 and 12 respectively. The pressure-increasing apparatus 5 consists of large- diameter side and small-diameter side cylinders 5a and 5b and a piston 5c moving slidably inside, and compressed fuel in the pressure chamber 4 is introduced into the large-diameter side cylinder 5a, while the fuel compressed in the groove 3a is introduced into the small-diameter side cylinder 5b. And the fuel introduced into the small-diameter side cylinder 5b is compressed to have high pressure under the pressure applied to the large-diameter side cylinder 5a, and the fuel of high pressure thus obtained is injected from the injection nozzle 10.