PURPOSE: To provide a display device generating a dot clock corresponding to a video signal with high versatility.

CONSTITUTION: The display device generates the dot clock signal based on an inputted horizontal synchronizing signal Hsync and can receive a different video frequency signal by using a phase sinchronizing circuit having a phase comparator circuit 3, a low pass filter 4, a voltage controlled oscillator 5 and a frequency divider circuit 2. The device is provided with a CPU1 detecting the frequency FHsync of the inputted horizontal synchronizing signal Hsync, deciding a dividing ratio N corresponding to the detected frequency FHsync and setting the decided dividing ratio N to the frequency divider circuit 2, and a divided signal based on the dividing ratio N and the horizontal synchronizing signal Hsync are phase-comparated then the dot clock signal based on the dividing ratio is generated.