A control device for an engine, which includes a plurality of cylinders, an electronically controlled unit injector for injecting fuel into each cylinder, and an electronically controlled valve train for opening and closing an intake valve and an exhaust valve of each cylinder, comprises an operating state detection unit for detecting the operating state of the engine, and electronic control units for performing an idle cut operation, in which fuel injection into some of the cylinders is stopped, and the intake valve and the exhaust valve of the cylinder concerned are kept closed, if the signal switching time is long when the idling of the engine of a vehicle waiting at traffic lights is detected by the operating state detection unit.