PURPOSE: To improve the total thermal efficiency of an internal combustion engine by recovering a part of exhaust gas energy as a motive power.

CONSTITUTION: The motive power of an internal combustion engine 1 rotates and drives paddle wheel 8 through its driving shaft systems 2 through 7. On the other hand, exhaust gas generated by the internal combustion engine 1 is led to an exhaust gas boiler via an exhaust gas conduit pipe 10, and generates steam by the heat retained. Then, the exhaust gas is discharged to the atmosphere through a chimney 12. Steam generated in an exhaust gas boiler 11 operates a steam engine 14, and generated energy is transmitted to a crank mechanism 15 through a driving shaft 14a to rotate and drive the paddle wheel 8 by means of paddle wheel driving shaft 16. Steam discharged from the steam engine is discharged into the chimney 12 to promote the drafting effect of the chimney.