To recover energy of exhaust gas and assist an engine without having a large impact on a transmission, by adding the relatively small number of parts and securing a relatively small space.

A power turbine 17 is disposed downstream the exhaust gas from a main turbine 15b of a turbo supercharger 15 which is disposed to an exhaust passage 14, and a power shaft 17a of the power turbine is connected with a crankshaft 10a of the engine 10 through a transmission 18. The transmission is provided with an eddy current coupling 21. A rotary magnetic body of the eddy current coupling 21 is connected with a crankshaft through a gear train 22, and is in a shape of disc in which a plurality of permanent magnet pieces are disposed so that their south poles and their north poles are alternately arranged per a predetermined angle in a circumferential direction. A rotary conductor of the eddy current coupling is connected with the power shaft through the gear train, and is spaced from the rotary magnetic body by a predetermined space, and is relatively rotatable with respect to the rotary magnetic body.