PURPOSE: To improve the frequency accuracy at an ultrahigh frequency band by using 1st and 2nd frequency converters so as to convert a frequency from the 1st and 2nd crystal oscillators, using 1st and 2nd detectors so as to detect the signal and outputting a difference between the detected signals in terms of voltage information.

CONSTITUTION: A 1st sampling phase detector 3 converts a frequency of a detected signal with a 1st reference signal based on a signal from a 1st crystal oscillator 1 and a 1st low pass filter 8 provides the frequency characteristic. Then a 1st detector 5 detects the signal from the 1st sampling phase detector 3. Similarly, a 2nd detector 6 detects a signal from the 2nd sampling phase detector 4. Moreover, a differential amplifier 7 outputs the difference between detection signals as to each detection signal from the 1st and 2nd detectors 5, 6 in terms of voltage information. Thus, the frequency discrimination characteristic C is obtained and a frequency fIN between different frequencies f1, f2 is recognized from the voltage.