PURPOSE: To prevent seizure between a cylinder and a plunger by forming a lubricating oil flow path, which communicates with a cam chamber to guide engine lubricating oil in the cam chamber, in the peripheral part of the plunger inserted into a cylinder body.

CONSTITUTION: After an engine is started, engine lubricating oil is guided into a cam chamber 11 from a lubricating route, and because the oil, which lubricates each sliding part of the engine, is heated, the engine lubricating oil in the cam chamber 11 is heated to a temperature higher than injection fuel. Here a cylinder 22, because of an inflow of the engine lubricating oil at a high temperature in each lubricating flow path 29 extension-formed in the axial direction in the cylinder 22 along a plunger hole 23, is heated to a high temperature as compared with a cylinder in which the lubricating oil flow path 29 is not formed. Accordingly, a differential temperature, generated between the cylinder 22 and a plunger 19, is decreased by guiding the engine lubricating oil in the car chamber 11, and seizure between the cylinder 22 and the plunger 19 can be prevented by suppressing the reduction of a clearance due to the differential temperature.