PURPOSE: To provide a simple, strong, and inexpensive super-high pressure hydraulic pump by forming an oil passage on an intermediate support body for communicating a discharge port of a first stage pump with a suction port of a second stage gear pump and forming serially multistage hydraulic circuits.
CONSTITUTION: When a driving shaft 9 is driven by external power, a driven gear is driven by means of a first stage drive gear, and a second stage drive gear 7 is driven by a spline shaft integrated with a shaft of the first stage drive gear 5, and thereby a second stage driven gear is driven. When whole of the gear is driven, operation oil is suctioned into a first stage gear chamber 2 from an operation tank through a suction port 31 and suction oil passages 32, 33. The oil is then increased in pressure and suctioned into a second gear chamber 3 through a discharge passage 34, a circular communication oil passage 35, and a suction oil passage 36 lead to the second gear chamber 3. It is pressurized again and discharged to a discharge port 38 through a discharge oil passage 37.