PURPOSE: To reduce the dead volume of an injection system and prevent pressure loss by forming a sack hole axially at the end part of a plunger, connecting this sack hole to a delivery slit provided on the periphery of the plunger, and providing this sack hole with a single built-in delivery valve.

CONSTITUTION: An inlet slit 31 and an inlet port 32 are provided radially at a barrel 3 having a vertical hole 30 for fitting a plunger 4, and the inlet port 32 is communicated with a pump chamber A by an inlet passage 20. The barrel 3 is further provided with delivery ports 33 corresponding in number to cylinders, bored radially at equal spaces apart in positions more on the pump chamber side than the inlet port 32. The plunger 4 is provided with inlet slits 41 corresponding in number to the cylinders, on the upper peripheral surface corresponding to the inlet slit 31 of the barrel 3, and also one delivery slit 42 at a part corresponding to the delivery ports 33. A sack hole 40 is provided at the end face of the plunger 4. The bottom of the sack hole 40 is connected to the delivery slit 42 by a bent passage 43, and a delivery valve 8 is built in the sack hole 40.