Disclosed are an image display device and an image processing method thereof. A signal processing method of the image display device according to the present invention is a signal processing method of an image display device configured to receive an image having a varied vertical synchronization signal, including detecting an input synchronization signal using an input image clock, extracting an input vertical synchronization signal from the input synchronization signal, delaying the input vertical synchronization signal by a reference value of an output clock, continuously tracking a falling region of the delayed input vertical synchronization signal, and finally generating an output synchronization signal in which a vertical front porch is varied.