Disclosed is an apparatus for controlling a duty ratio of a signal that includes a clock control unit configured to generate a plurality of control signals based on an input signal, a half-cycle generation unit configured to generate a multiplied signal by use of the input signal and a delay signal that is obtained by delaying the input signal based on a delay control voltage, and divide the multiplied signal to generate a first division signal and a second division signal that are in inverse relation to each other, a comparator unit configured to compare a pulse width of the first division signal with a pulse width of the second division signal based on the control signal provided by the clock control unit, and output a delay control signal corresponding to a result of the comparison, and a control voltage generation unit configured to output a delay control voltage.