A PLL as a clock generation circuit that generates a PWM clock based on a reference clock, which PWM clock is used for controlling, in a pulse width modulation method, a lamp on time and a lamp off time of a light source illuminating a liquid crystal panel by synchronizing with a video signal that performs display in a set period on the liquid crystal panel, includes a configuration that generates a PWM clock that can maintain a fixed ratio of the lamp on time to the lamp off time within one period even if the set period is changed, by changing a pulse interval of the reference clock in conjunction with the change in the set period.