PURPOSE: To prevent unnecessary data from occurring much even if a received carrier level is large by deciding a compensating time based on the difference between the carrier level in the midst of being received and a specified level and transitting a carrier detection signal from ON to OFF after the compensating time passes when a carrier off decision means decides to be carrier off.

CONSTITUTION: A digital AGC circuit 1 and a level detection circuit 4 constitute the carrier off decision means 100, which has a function for deciding to be the carrier off when the received carrier level becomes less than a specified level. And the level detection circuit 4, a time control part 9 and a timer part 7 constitute a carrier detection signal control means 200, which has a function for deciding the compensating time based on the difference between the carrier level in the midst of being received and the specified level and transiting the carrier detection signal from ON to OFF after the compensating time passes it the carrier off decision means 100 decides to be the carrier off. Thus, the quantity of the occurrence of unnecessary data can be reduced when the carrier level becomes large.