To provide a pump device whose mechanism to adjust the discharge amount can be made small and simplified.

The pump device 1 equipped with a housing 2, a plunger 3, a pressurization chamber 4, etc. includes a rod inserting hole 31 formed in the plunger 3 stretching parallel with its axis, a control rod 5 which penetrates the pressurization chamber 42 from inserting holes 22d and 22e formed in the forefront part of the housing 2 and is inserted into the rod inserting hole 31 with possibility of position adjustment, an intra-rod passage 30 formed inside a part of the control rod 5 midway in its longitudinal direction, and a bypass 6 which has an intra-housing passage 32a to put the forefront part of the intra-rod passage 30 in communication with a suction port 25a and a base opening 30b able to put the base end of the intra-rod passage 30 in communication with the pressurization chamber 4 and can put the pressurization chamber 4 in communication with the suction port 25, whereby the discharge amount of working oil can be changed by adjusting the axial direction position of the control rod 5.