An image processing apparatus, which displays an image corresponding to a synchronizing frequency change-image signal, which is obtained by changing a frequency of a synchronizing signal of an image signal, and an other image corresponding to an other image signal on a same display screen. The apparatus comprises a monitoring device and a synchronizing control device. The monitoring device monitors temporal relationship between the synchronizing signal of the synchronizing frequency change-image signal and a synchronizing signal of the other image signal. The synchronizing control device performs frequency regulation for the synchronizing frequency change-image signal based on the monitoring results from the monitoring device so as to prevent one of the synchronizing frequency change-image signal and the other image signal from passing the other thereof on the display screen.