A pressure booster , 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 . <EOS>