A pressure booster (10, 10A, 10B), comprising: a pressure boosting chamber; a first drive chamber disposed on one end side of the pressure boosting chamber; a second drive chamber disposed on another end side of the pressure boosting chamber; a piston rod configured to penetrate through the pressure boosting chamber and extend to the first drive chamber and the second drive chamber; a pressure boosting piston which, by being connected to the piston rod inside the pressure boosting chamber, divides the pressure boosting chamber into a first pressure boosting chamber on a side of the first drive chamber, and a second pressure boosting chamber on a side of the second drive chamber; a first drive piston which, by being connected to one end of the piston rod inside the first drive chamber, divides the first drive chamber into a first pressurizing chamber on a side of the first pressure boosting chamber, and a second pressurizing chamber remote from the first pressure boosting chamber; a second drive piston which, by being connected to another end of the piston rod inside the second drive chamber, divides the second drive chamber into a third pressurizing chamber on a side of the second pressure boosting chamber, and a fourth pressurizing chamber remote from the second pressure boosting chamber; a fluid supplying mechanism configured to supply a fluid to at least one of the first pressure boosting chamber and the second pressure boosting chamber; a first discharge return mechanism configured to supply the fluid discharged from the first pressurizing chamber to the second pressurizing chamber, or to supply the fluid discharged from the second pressurizing chamber to the first pressurizing chamber; and a second discharge return mechanism configured to supply the fluid discharged from the third pressurizing chamber to the fourth pressurizing chamber, or to supply the fluid discharged from the fourth pressurizing chamber to the third pressurizing chamber. a pressure boosting chamber; a first drive chamber disposed on one end side of the pressure boosting chamber; a second drive chamber disposed on another end side of the pressure boosting chamber; a piston rod configured to penetrate through the pressure boosting chamber and extend to the first drive chamber and the second drive chamber; a pressure boosting piston which, by being connected to the piston rod inside the pressure boosting chamber, divides the pressure boosting chamber into a first pressure boosting chamber on a side of the first drive chamber, and a second pressure boosting chamber on a side of the second drive chamber; a first drive piston which, by being connected to one end of the piston rod inside the first drive chamber, divides the first drive chamber into a first pressurizing chamber on a side of the first pressure boosting chamber, and a second pressurizing chamber remote from the first pressure boosting chamber; a second drive piston which, by being connected to another end of the piston rod inside the second drive chamber, divides the second drive chamber into a third pressurizing chamber on a side of the second pressure boosting chamber, and a fourth pressurizing chamber remote from the second pressure boosting chamber; a fluid supplying mechanism configured to supply a fluid to at least one of the first pressure boosting chamber and the second pressure boosting chamber; a first discharge return mechanism configured to supply the fluid discharged from the first pressurizing chamber to the second pressurizing chamber, or to supply the fluid discharged from the second pressurizing chamber to the first pressurizing chamber; and a second discharge return mechanism configured to supply the fluid discharged from the third pressurizing chamber to the fourth pressurizing chamber, or to supply the fluid discharged from the fourth pressurizing chamber to the third pressurizing chamber.