To provide an inverter transformer capable of detecting in high precision an open state of a secondary side load while having a simple and low cost structure, and to provide a discharge lamp lighting device that uses the inverter transformer.

The discharge lamp lighting device 20 is equipped with an inverter transformer T1, a full-bridge circuit 23, and a control circuit 22, and discharge lamps La21, La22 are connected to the output terminals on secondary winding high-voltage side of the inverter transformer T1, and by applying an AC voltage to the discharge lamps La21, La22, they are lit. Detection terminals 13, 13a are provided in the vicinity of the output terminals, on the secondary winding high-voltage side of the inverter transformer T1; and according to these, an abnormal voltage induced by an open state of the secondary side load is detected, and by feeding back a signal, based on this abnormal voltage to the control circuit 22, the operation of the full-bridge circuit 23 is stopped.