PURPOSE: To perform combustion with a lean mixture, by heating secondary air with thermal energy of exhaust gas and introducing the secondary air to an intake pipe.

CONSTITUTION: The outside air is sucked from an air cleaner 31 to open a check valve 28, circulated flowing in an air pipe 17 from a pipe 20' and heated by exhaust gas, then the heated air is sucked into an injection flange 8 from a heat resisting pipe 20 and jetted into an intake manifold 10 from an injection hole. A mixture is heated by this hot air, expanded and changed to a lean state, then a mixture not in a vaporized state can be completely gasified and completely performed combustion in a cylinder.