PURPOSE: To raise the combustion efficiency of an internal combustion engine of the type disposed in a heating medium charged in a container and to achieve energy saving of the engine, by disposing an intake pipe and an exhaust pipe coaxially with each other, and feeding combustion air heated by the heat of exhaust gas.

CONSTITUTION: An exhaust pipe 9 connected to the exhaust port of an internal combustion engine 3 and having a smaller diameter than an intake pipe 8 is disposed coaxially on the inside of the intake pipe 8 which is connected to the intake port of the engine 3. The exhaust pipe 9 is inserted into the intake pipe 8 at its root portion. An intake unit 82 incorporating therein a ring-like air filter 81 is attached to the top of the intake pipe 8, and combustion air is drawn into the intake pipe 8 from an intake opening 83 via the air filter 81. Here, the exhaust pipe 9 is longer and has a smaller diameter than the intake pipe 8, so that it is extended through the intake unit 82 and projected upward from the same.