PURPOSE: To reduce non-detection/mis-detection of a unique word and to improve the reliability by controlling an error permission rate of detecting the unique word in a unique word detection means through the detection of power.

CONSTITUTION: An estimated power of a received RF signal being one burst signal from an RF power measurement device 6 is received by a unique word detector 5 to control an error permissible range in the detection of the unique word. That is, when the power of the received RF signal of the present burst is extremely smaller than the power of the preceding burst, it is highly possible that the data pattern sent in the preceding burst is postamble data, then an error permissible range in the unique word detector 5 is extended. When the power of the reception RF signal of the current burst is extremely larger than the power of the preceding burst, since the probability of the data pattern sent in the burst to be preamble data is high, the error permissible range in the unique word detector 5 is extended.