A liquid crystal display device is provided which is capable of preventing flicker or fringes in a display screen occurring even when changes in frequencies of a vertical sync signal and horizontal sync signal contained in a video signal input to the liquid crystal display device occur. A frequency detecting circuit sets a frequency of a driving pulse voltage at a value in the vicinity of "positive integer+1/2" times of the frequency of the horizontal sync signal and a pulse frequency for PWM (Pulse Width Modulation) light control at a value in the vicinity of a positive integral multiple or "positive integer+1/2" times of the vertical sync signal and a resonant frequency at a value in the vicinity of the frequency of the driving pulse voltage by adjusting capacitance value of a resonant capacitor.