PURPOSE: To prevent malfunction due to incorrect data caused by the disturbance of received signals which is apt to occur at the time of starting reception by making data from starting of reception for a specified time invalid.

CONSTITUTION: When a receiving detection circuit 2 detects start of inputting of received signals to a demodulating circuit 1 basing on a time element signal RxC from the demodulating signal 1, the detection circuit outputs a receiving detection signal 9 and starts an incorrect data prohibition signal generating circuit 3. The incorrect data prohibition signal generating circuit 3 has a timer circuit, and sends an incorrect data prohibition signal (b) to a gate 4 for received data from inputting of the receiving detection signal (b) over a specified time and prohibits inputting of a data element signal RxD to a data processing device 5. The incorrect data prohibition signal generating circuit 3 is set to generate the incorrect data prohibition signal (b) from the start of receiving of received signals over a specified time in which disturbance of received signals is restored. From a time when generation of the incorrect data prohibition signal b is terminated the data element signal RxD from the demodulating circuit 1 is inputted to the data processing device 5 through the gate 4 for received data.