PURPOSE: To make it possible to use selectively the gaseous fuel or liquid fuel, by mounting a means to introduce liquid fuel or gaseous fuel selectively and a means to ignite bodh an electric heater heating a heat storing wall and a mixture of jetted fuel and air.

CONSTITUTION: At first an electric current is supplied to sheath heater, when liquid fuel is to be used. As the electric current is supplied to the sheath heater, a heat storing wall 4 is gradually heated to a high temperature. When the desired temperature is reached, the feed of gaseous fuel is suspended and instead the liquid fuel is fed by opening an electromagnetic valve and driving a pump. The liquid fuel drops on the outer surface of the greater diameter part 15 of an air guide cylinder 14 through a pipe 23. Then they are scattered to the inner part of the caplike part in the heat storing wall 4. Because the cap 8 is maintained at a high temperature owing to the heating of sheath heater, the fuel scattered is quickly vaporized. The vaporized gas fuel is mixed with air by an agitating blade 18 and jetted through the jet hole, and the ignition is made by the electrode 26.