PURPOSE: To prevent mis-decision by providing a memory storing the relation among reception wave levels of a desired reception channel and adjacent channel, the output of an out-band noise measuring section and the output of an envelope detector in advance and referencing the memory to decide whether the received wave is on the desired channel or the adjacent channel.

CONSTITUTION: A computer 12 obtains a received wave level Bd when the received wave is a desired channel wave and the received wave level Bu when the wave is the adjacent channel wave from the level of an out-band noise output 6 and obtains the received wavelevel Dd when the wave is the desired channel wave and the received wave level Du when the wave is the adjacent channel wave from the received envelope level of the received envelope output 9. Then the Bd and the Dd, and the Bu and the Du are compared respectively, and when Bd=Dd, it is decided that the input wave is the desired channel wave and when Bu=Du, it is decided that the received wave is the adjacent channel wave. The result of decision is outputted to the decision output terminal 14. Then the received wave level is outputted to a received electric field level output terminal 15 at the same time.