To stabilize the quantity of fuel delivered to an intake passage by preventing fuel vapor from being delivered from a fixed fuel chamber of a carburetor to an intake passage, and keeping constant the fuel pressure of the fixed fuel chamber.

In this fuel pressure regulator of the carburetor, a crank chamber of an engine or a discharge chamber 31 of a fuel pump 21 taking the pulsating pressure generated in an intake pipe as the driving force and a fuel tank 35 are connected by a relief passage 41, and a pressure regulating valve 42 for discharging the pressure above a preset value in the discharge chamber 31 to the fuel tank 35 is provided in the relief passage 41, whereby when the pump discharge fuel pressure is high, some of fuel is discharged with fuel vapor generated in the fuel pump 21 to the fuel tank 35, only the fuel having preset pressure is fed into the fixed fuel chamber 7 to prevent the generation of fuel vapor in the interior thereof, and the quantity of fuel delivered to the intake passage 3 is stabilized.