An igniter transformer includes a secondary coil and a primary coil which are
closely coupled. A plurality of round single-core wires disposed substantially
parallel to one another in a common plane are bonded side by side to form a flat
multicore wire that is substantially rectangular in cross-section. The secondary
coil includes the flat multicore wire which is edgewise wound such that the larger
surfaces of the flat multicore wire face each other in the turns while standing
upright. The primary coil includes a wide thin metal sheet wound substantially
perpendicularly to an axis of the secondary coil.