PURPOSE: To suppress reception interference by using a signal obtained by means of diffusing a frequency in a clock signal.

CONSTITUTION: A directional antenna 1 detects a direction. A local oscillation part 3 and a control processing part 4 in a frequency synthesizer which sets the output of a liquid crystal oscillator 5 to be reference controls the reception frequency of a reception part 2. The processing part 4 processes on azimuth signal which the reception part 2 amplified and detected in terms of azimuth calculation. A clock signal generator 6 impresses a saw tooth wave generated in a multi vibrator 7 on a voltage controlled oscillator 9 through an RC filter 8 and generates it at the clock signal which has been frequency-modulated. When the frequency of the clock signal is diffused, the head value is reduced at a rate that the frequency is diffused in proportional to that of a single frequency. Since the high frequency component of the clock signal which gives interruption to the reception device is diffused by the multiple, the degree of interruption given to the reception device which receives signals at a narrow reception band width is reduced.