To prevent the deterioration of exhaust emission at transitional operation time, and enhance operability by communicating an elastic chamber whose volume expands and contracts in response to driving reaction to the delay angle side in a force feed stroke of a plunger with a timer piston high pressure chamber, and opening a valve to open and close its communicating passage in a rotation area requiring a low injection rate.

A cylinder 52 to communicate with a high pressure chamber 37 through a passage 51 is arranged on the opposite side of the timer piston 33 side of the high pressure chamber 37, and the inside of the cylinder 52 is partitioned into two chambers by a piston 53 to be slidably inserted into this cylinder 52. An elastic chamber 54 to communicate with the high pressure chamber 37 is arranged in one among these two chambers, and a spring 56 is housed in the other chamber 55. An always closed injection rate control valve 58 is arranged in the passage 51, and this control valve 58 is opened in a rotation area requiring a low injection rate by a signal from a controller. Therefore, operating fluid flowing in the elastic chamber according to a finish of fuel injection flows in the timer piston high pressure side, and returns to a position before force feed, and can be changed to a low injection rate.