PURPOSE: To secure the automatic selection and switching for the input signal as well as enhance the controllability of the device, by giving the priority of transmission only to the input signal that arrives last in case more than two input signals are supplied.

CONSTITUTION: In case input signal S2 is applied to input terminal 2 in the state under which input signal S1 is applied to input terminal 1 with switch circuit 4 closed, signal S2 is converted 8 into binary coded signal E2 to supplied to memory circuit 10. At circuit 10 the priority is given to the binary signal (E2 in this case) which is supplied later and control signal CS1 is changed into zero forcedly, and at the same time control signal CS2 is delivered to switch circuit 5. As a result, circuit 4 closed hitherto is opened to break the transmission of signal S1, and at the same time circuit 5 is opened. And only signal S2 (supplied last) from terminal 2 is delivered through terminal 11 via circuit 5.