PURPOSE: To eliminate pressure fluctuation, prevent vibration and noise from a device, and prolong the service life of a directional control valve in a hydraulic drive type high pressure fluid generating device for high pressure fluid in which two stepped piston type reciprocating boosters are used.

CONSTITUTION: The position of a piston of two stepped piston type reciprocating boosters is detected by limit switches 21 to 24 and, according to the signals i1 to i4 transmitted from the limit switches, drive signals S1 to S14 are output, respectively, on a specified schedule. The drive signals are input into an electromagnetic drive section to control directional control valves 3 and 4 so that their operation phases are reversed to each other. Thus the pressure of a high pressure fluid obtained by combining fluids discharged from the boosters is set roughly at a constant and, by making a series of operations continuously and repeatedly, a high pressure fluid free from pressure fluctuation can be obtained stably.