PURPOSE: To variably set a ctank angle range within a specified value in a plunger pump, under the state that a discharge pressure is a specified value or more in a discharge process.

CONSTITUTION: An axial through-hole 60 is formed in a plunger 42 and faced to a pump chamber 24 through a window 62 on a leading end of the plunger 42. A first piston 66 prevents escaping by a peripheral edge of the window 62, and is slidably arranged in the axial through-hole 60. A compressive coil spring 76 is compressed between a first piston 66 and a stopper 70. The first piston 66 is energized to the side of the window 62. At the initial time of discharge process, the first piston, under restriction of the stopper 70, is separated from the window 62 against energizing force of the compression coil spring 76.