PURPOSE: To enable to vaporize liquefied petroleum gas (LPG) effectively, by disposing a primary pressure reducing regulator and a secondary pressure reducing regulator between an LPG cylinder and a mixer successively from the upstream side and in series to each other, and fixing an electric heater to the bottom of a pressure reducing chamber of the primary pressure reducing regulator.

CONSTITUTION: A water heater 5, a primary pressure reducing regulator 6 and a secondary pressure governor 7 are disposed successively from the upstream side of an LPG passage 4 at the portion thereof located between an LPG cylinder 1 and a mixer 2 for mixing air and LPG. Further, an electric heater 36 is fixed to the bottom wall of a case 20 for the regulator 6, and its heating element 37 is projected upward from the bottom surface of a primary pressure reducing chamber 24. The heating element 37 is connected to a power source 84 via a controller 83. Here, arrangement is such that current is supplied to the heating element 37 when the engine temperature is low, for instance, in response to the output signal of a sensor 85 for detecting the temperature in the engine room.