A cold-cathode tube drive device includes an inverter circuit (1) for generating a high-frequency voltage, a booster transformer (2) for boosting the high-frequency voltage generated by the inverter circuit (1), a cold-cathode tube (3) which is turned on by the high-frequency voltage after boosted by the booster transformer (2), a series circuit (6) having a reactance element (4) connected in parallel to the cold-cathode tube (3), a synthesis circuit (8) for combining the connected current value i2 of the series circuit (6) with the secondary side current value i1 of the booster transformer (2) so as to indirectly detect the lamp current value iL of the cold-cathode tube (3), and a control circuit (9) for controlling the inverter circuit (1) according to the lamp current value iL indirectly detected by the synthesis circuit (8) and controlling the lamp current of the cold-cathode tube (3).