PURPOSE: To accurately drive an exhaust control valve by providing a drive source therefor above a flywheel cover laid at a position opposite to a pulley for driving the auxiliaries of an engine body.

CONSTITUTION: An exhaust control valve for variably controlling a compression ratio or exhaust timing is provided in a direction orthogonal with the axial direction of cylinder bore, thereby opening and closing each sub-exhaust passage. Furthermore, a drive device 30 for actuating the exhaust control valve is laid above a flywheel cover 23. A pulley 21 to drive auxiliaries is provided at one side of an engine body along the direction of a crankshaft 7. A flywheel 22 is laid at the other side of the engine body along the direction of the crankshaft 7 and enclosed with the flywheel cover 23. The drive device 30 is constituted of a motor and a gear train thereby rotated. Thus, the motor and the exhaust control valve can be arranged to be near each other, and the exhaust control valve can be actuated without any need of a wire or the like. According to this construction, the exhaust control valve can be accurately driven.