To provide a hydraulic intensifier with a miniaturized pump, dispensing with a selector valve, and having less noise to be generated.

The hydraulic intensifier comprises two boosters 5, 5'; each booster being equipped with pressure pumps 11, 11' to supply the booster with a low pressure fluid A. The booster is also equipped with a low pressure side cylinder 53 and a high pressure side cylinder 54. The low pressure side cylinder is divided by a low pressure side piston 55a into a primary side space 53a and secondary side space 53b. The low pressure side piston is integratedly structured with a high pressure side piston 55b. The pressure pump 11 which rotates in either normal and reverse directions is connected to the primary side space of the low pressure side cylinder and the secondary side space of the low pressure side cylinder is connected to a pressurizer 13. The normal rotation of the pressure pump 11 feeds the fluid A into the primary space 53a while pressurizing fluid B in the high pressure side cylinder 54. The reverse rotation of the pressure pump 11 effects the gas in the pressurizer 13 to enter into the secondary side space 53b, thereby ascending the piston 55 while sucking the fluid B into the high pressure side cylinder 54.