PURPOSE: To automatically track an illegal station by the parameter of radio waves and to automatically record the data of radio wave emitting time and emitting direction when the illegal station is found.

CONSTITUTION: The radio waves are received by an antenna 10 and the parameter of the received radio waves is obtained by parameter detection circuits 20 and 22. A disk 28 stores the parameter of the radio waves from the illegal station obtained beforehand and a collation means 30 compares the parameter of the received radio waves with the stored parameter. When the compared result is coincident, frequency-to-amplitude data and the time at the time of reception are stored in the disk 28 and the audio signals of the radio waves at the time are recorded in a recorder 38. Also when the compared result is non-coincident, the reception of the radio waves and the detection of the parameter are returned and the same processing is repeated. Also, when it is judged that the received radio waves are the radio waves from the illegal station, by using direction finders 44, 46 and 48, the emitting direction of the received radio waves is obtained and the data of the obtained direction are stored as well.