Abstract: An inverter transformer for lighting multiple discharge lamps is provided which has a plurality of output voltages including reversed polarity output voltages while ensuring a reliable insulation performance, and which is produced in a small size and at a low cost. An inverter transformer includes a magnetic core assembly, and a plurality of bobbins each having a primary winding and a secondary winding wound therearound. Adjacent two bobbins of the bobbins constitute either a first bobbin pair which are provided with respective secondary windings at which output voltages having their polarities reversed from each other are induced, or a second bobbin pair. An insulation distance setting means are provided between the two bobbins so that the distance between the secondary windings disposed at the two bobbins and of the first bobbin pair is larger than the distance between the secondary windings disposed at the two bobbins of the second bobbin pair.