PURPOSE: To always accurately output a beacon signal having the same transmitting frequency as that of a radar signal by providing switching means for selecting any of a radar frequency signal and a transmitting frequency signal, etc.

CONSTITUTION: A radar signal is received by receiving means 1, control means 14 connects switching means 5 to a radar frequency signal side, switching means 6 to the means 5 side and switching means 16 to radar frequency storage means 7 side. When radar frequency corresponding voltage data is stored in the means 7, the means 14 switches to connect the means 5 to a transmitting frequency signal side and the means 16 to the side of storage means 8 for a folded frequency. Thus, a transmitting frequency signal from voltage control oscillating means 3 is folded to be input and converted to frequency/voltage converting means 2 via the means 6, 5, and further ADD-converted by an A/D converter 17. The folded frequency corresponding voltage data is input and stored in the means 8 via the means 16, and compared with data of the means 7.