The present invention relates to an oscillator that is capable of realizing duty balancing.The oscillator determines a switching frequency of a converter converting an input voltage according to a switching operation of switches to generate an output voltage.The oscillator determines a first half cycle of a duty signal determining the switching frequency by using a reference current according to a feedback signal corresponding to the output voltage. The oscillator senses a first half cycle period by using an output of the frequency setting unit, and determines the same period as the first half cycle as a second half cycle of the duty signal after the first half cycle.