The present invention relates to a lamp ballast circuit and a driving method. The lamp ballast circuit includes a voltage detector for detecting the level of a first voltage corresponding to an input voltage, a controller including an oscillator for changing the oscillation frequency according to the level of the first voltage, and an output unit for changing the frequency of the output voltage in correspondence to the oscillation frequency. Therefore, a lamp ballast circuit having less power consumption and that is operable by a lesser input current with less THD and a driving method thereof are realized.