PURPOSE: To improve a lighting property without changing luminance and power consumption by controlling the power source of an inverter, converting a direct current into an alternating current to be applied to a cold cathode tube, to make lighting voltage higher at the time of low temperature than that at the time of ordinary temperature and shorten the lighting period of dimming.

CONSTITUTION: A voltage control circuit 1 and a dimming circuit 3 use respective switching regulators 8 and 9 to control transistors 2 and 4 to control the connection/disconnection of input voltage and electric power to an inverter 5. Corresponding to this input voltage and connection/disconnection, the inverter 5 applies A.C. voltage of a constant frequency to a cold cathode tube 6 with which a temperature sensor 7 is made in contact to light the cold cathode tube 6. Associating with the detected temperature of a sensor 7, in low temperature more than in ordinary temperature, the circuit 1 increases output voltage, and the circuit 3 shortens the period of the connection of dimming by the connection/disconnection set by a variable resistor 10. This can improve the lighting property of the cold cathode tube 6 in low temperature without changing luminance set at initial stage and power consumption.