If it is determined that an engine has been started, an engine coolant temperature is detected. If the engine coolant temperature is equal to or lower than a threshold value, the catalyst quick warm-up control is started to retard ignition timing, and a signal indicating a command to increase an operate angle is transmitted to a VVLA controller. When a VVT hydraulic pressure is increased to a predetermined value, a signal indicating a command to decrease the operate angle is transmitted to the VVLA controller, and a signal indicating a command to advance open timing of an intake valve is transmitted to a VVT controller so that the open timing of the intake valve is not changed. If the engine coolant temperature is equal to or higher than a threshold value, the catalyst quick warm-up control ends, and the ignition timing is returned to normal timing.