having strong catalytic action with hydrocarbons such as fuel and may be in the form of a platinum wire or a platinum and or palladium film deposited on the surface of a member having a shape similar to glow plugs of the type used in diesel engines the heater 58 is supplied with electric current to have a surface temperature of 300 u00b0 c or more for catalytic action preferably the inner surface of the flame stabilizing cover 62 has a catalytic action the flame stabilizing cover 62 serves to protect against local combustion of the mixture and promote passage of the mixture to stabilize the combustion it was ascertained through experiments that the local combustion cannot expand over the whole mixture preferably the heater 58 is made to have a small heat capacity so that the local combustion can be stopped immediately when the electric current to the heater 58 is cut off for this purpose the heater 58 may be taken in the form of a thin platinum wire in the second embodiment the control unit 40 is responsive to various engine operating factor indicative signals a to g to provide control signals h and i to the main and auxiliary fuel flow control valves 26 and 36 so as to provide an optimum air fuel ratio corresponding to the engine operating condition the air fuel ratio sensor 56 detects the axtual air fuel ratio of the mixture supplied to the engine and provides an air fuel ratio indicative signal to the control unit 40 for feedback contol of the air fuel ratio thus it is possible to provide an optimum air fuel ratio corresponding.