Satisfactory restartability has not been obtained so far because the timing of opening an exhaust valve of a cylinder under expansion stroke is adjusted for improvement of startability and a valve adjusting mechanism is always controlled in the same manner regardless of the engine status at start. In the invention, control is performed to adjust the timing of closing an intake valve so that an effective compression ratio of a cylinder under compression stroke reduces. Also, the effective compression ratio of the compression stroke cylinder is decided based on a piston position at engine restart. By varying the intake valve closing timing in the expansion stroke cylinder to reduce the effective compression ratio depending on the engine status at restart, it is possible to lessen a load imposed on a starter when the engine is restarted, and to improve startability without complicating the engine system.