Received videos through A and B routes are inputted in first and second variable devices and then delayed by a first and a second frame memory by one frame to be inputted in a comparator. Alternatively, these signals A and B are further delayed by one frame by third and forth frame memories and also inputted in the comparator. The comparator compares the signals obtained by delaying the signals A, B, AF and BF by one line and one pixel, respectively, between the A and B routes with respect to all combinations so as to detect the difference between them. Then, a signal having the minimum difference is detected and a first and a second memory control signal to make the difference smaller are outputted to the first and second variable delay devices. By repeating the processing, a horizontal difference, a vertical difference and a time axial difference are gradually, and then completely, corrected including when the original amount of the difference is larger than a frame delay.