PURPOSE: To perform automatic changeover corresponding to an input signal with high reliability and to eliminate complicated operation by obtaining a switching signal by passing the compared result of counted data and preset data through transformation matrix.

CONSTITUTION: A horizontal synchronizing signal 1 is inputted to a first counter 5 as a reset signal and a counted result is transmitted to first and second comparators 7 and 8 until counting is reset by the signal 1 with an output pulse from a first oscillation circuit 3 as a clock. Similarly, a vertical synchronizing signal 2 is inputted to the second counter 6 and the counted result is sent to the third comparator 9 until the counting is reset by the signal 2 with the output pulse from the second oscillation circuit 4 as the clock. In the meantime, a comparing data setting circuit 10 presets prescribed values at the comparators 7-9 at the time of starting power supply. Then, the comparators 7-9 compare the values with the counted results from the counters 5 and 6 and transmit logic signals. On the other hand, a transformation matrix circuit 11 is a so called ROM and outputs the switching signal 12 by a transformation rule based on the logic signals from the comparators 7-9.