A pulse width modulation (PWM) wave output circuit that efficiently and accurately outputs dual PWM waves includes two comparators, an OR circuit, and an AND circuit. A voltage generator supplies the comparators with ramp voltages having the same wave height and shifted phases. The comparator compares the ramp voltages with the reference voltage and provides the comparison results to the OR circuit and the AND circuit. The OR circuit outputs a first modulation wave, and the AND circuit generates a second modulation wave. Accordingly, modulation waves having different duties are output based on ramp voltage having different phases.