PURPOSE: To perform the heating and cooling of fuel so accurately, by setting hydrogen-occluded metal to the underside of a carburetor flat chamber, while controlling the adsorption and discharge of hydrogen to and from this metal according to fuel temperature inside the float chamber.

CONSTITUTION: A concave part 2d is installed in the underside of a float chamber 2 of a carburetor 1, while a hydrogen-occluded metal 7a is set to the inside, and connected to the same kind of another hydrogen-occluded metal 14a being set in a cooling passage through a pipe 18 having an on-off value 17 at the point midway. When temperature of fuel inside the float chamber 2 is low, the valve 17 is opened by a signal out of a temperature detector 5, and with selection of refrigerant passage selector valves 15a and 15b, a refrigerant for cooling air, cooling water, etc., is selected to a bypass passage 16, whereby high pressure hydrogen at the side of the metal 14 moves to the metal 7a, thus the metal 7a generates heat for heating the fuel. When fuel temperature is high, these selector valves 15a and 15b are selected to where they should be, cooling the metal 14 and raising a degree of hydrogen occlusion capacity, and hydrogen is discharge out of the metal 7 so that the metal is cooled, cooling the fuel in this way.