An apparatus for regulating fuel supply to a liquefied petroleum gas engine comprising a housing divided by a lower chamber passing through the fuel in liquid phase from a fuel supply to a vaporizer and an upper chamber connected to a carburetor of the engine passing through the fuel in gas phase from the vaporizer to the carburetor by a partition wall having a passage therein, the composition of the fuel being determined in temperature and vapor pressure of the fuel in liquid phase in the lower chamber, the flow of the fuel in gas phase from the passage in the partition wall to the upper chamber being controlled by valve means actuated in response to the temperature and the pressure of the fuel in liquid phase.