Abstract: A structure for facilitating the starting and warming of an internal combustion engine provided with a carburetor in its intake passage. A side passage which is separate from the intake passage by-passes a throttle valve in the carburetor is connected to the intake passage. A fuel nozzle capable of injecting fuel into the side passage and a control valve adapted to open and close the side passage are also provided. A heating chamber is formed in the side passage on the downstream side of the control valve. A heating element adapted to heat a gaseous mixture generated in the side passage to turn the gaseous mixture into a combustible gaseous mixture is accommodated in the heating chamber. The structure may further include a heat insulating member inserted between the heating chamber and carburetor and/or intake passage. Further, the structure may include a secondary air passage, a fuel injection unit for injecting fuel into the heating chamber and a catalytic converter in the heating chamber.