An image display device well suited for a multi-scanning type monitor includes a video signal measurement circuit that detects a horizontal synchronization frequency fH and a vertical synchronization frequency fV from an input image signal that conforms to the GTF Standard. A main control portion calculates timing data relative to a waveform of the signal (21) using the frequencies fH and fV, calculates adjustment parameters for adjusting a size and a position using this timing data, and sets the adjustment parameters to deflection control circuits, so that an image of the image signal may be displayed well on a CRT. Since the timing data is calculated using the synchronization frequencies fH and fV of the input image signal, it is possible to save on a memory capacity without storing timing data that corresponds to a plurality of different kinds of image signals.