An ECU varies a period during which an intake valve and an exhaust valve are both simultaneously open by setting a target overlap angle OVP to be equal to a limit overlap angle OVL until the coolant temperature becomes higher than a reference temperature to reduce the internal EGR amount. The data is processed on a sequential element basis where each element has a pre-determined number of bits M which bits are contained in a block of sequential data words W\u2032. In a first embodiment, the respective plurality of windings connected parallel to one another are located next to one another on a core of the pulse transformer, and are wound around the core such that the coupling of the primary windings to the secondary winding is increased. The central portion is formed of a nitride insulating film containing at least nitrogen, and both end portions are each formed of an oxide insulating film containing oxygen and no nitrogen. The centering of the optical element is performed with the aid of the engravings.