PURPOSE: To prevent a signal interference inside an IC constituted of an ECL for selecting and processing one of plural signals.

CONSTITUTION: FM signals SG 1 and SG 2 are inputted to the respective input terminals of a selecting IC 4 constituted of the ECL via signalling ICs 1 and 2 constituted of the ECL. The positive and negative polarity output terminals of a controlling IC 3 constituted of the ECL are commonly connected to their corresponding output terminals of the signalling ICs 1 and 2. At the input terminal of the selecting IC 4, when the output of the controlling IC 3 becomes a high level, this input terminal side becomes a constant DC level irrespective of the FM signal. Further, when the output of the controlling IC 3 becomes a low level, an input signal is transmitted by the input terminal side corresponding to this.