A control device is configured to read a required operation point of the internal combustion engine at the moment of restart following after intermittent stoppage, and to execute, when it is determined that the required operation point belongs to a reduced-cylinder operation allowed region and also to a reduced-cylinder operation restricted region which lies on a high load side of the reduced-cylinder operation allowed region, an all-cylinder operation and then move into a reduced-cylinder operation. When it is determined that the required operation point belongs to the reduced-cylinder operation allowed region but not to the reduced-cylinder operation restricted region, the control device is configured to switch the engine to the reduced-cylinder operation without execution of the all-cylinder operation.