PURPOSE: To raise engine efficiency and reduce exhaust emission by connecting an internal combustion engine and a motor/generator with a piston rod, and synchronously controlling movements thereof in accordance with a signal from a position indicator with a computer.

CONSTITUTION: A computer 19 supplies the current from a battery to a motor/ generator comprising a permanent magnet 12, a yoke 16 and a coil 17 in accordance with the piston position from a position indicator 18, moves a piston 10 toward an upper dead point further than in the compression stroke for exhausting exhaust gas, and then moves the piston to the opposite side to intake mixed gas. The piston 10 is then driven toward the upper dead point for compression and ignition at a predetermined timing. In the combustion stroke, the piston 10 makes the permanent magnet 12 function as a generator rotor. The power generated from the coil 17 is charged to a battery. The above- mentioned movement is repeated. Mechanical power is obtained from the movement of the piston 10. Thus, it is possible to improve fuel consumption and reduce exhaust emission.