To reduce worsening of phase noise characteristics due to mechanical vibrations.

A 1st crystal vibrator 1a and a 2nd crystal vibrator 2 having a same characteristics are mounted closely in the same direction, an amplifier 3 and an inverter 4 inversely amplify the output of the 2nd crystal vibrator 2 and its output signal controls a VCXO (voltage-controlled crystal vibrator) 1 consisting of the 1st crystal vibrator 1a. Thus, an inverted voltage in response to vibration generated from the 2nd crystal vibrator 2 through a piezoelectric effect by mechanical vibrations exerted to the 2nd crystal vibrator 2 is used to control the oscillating frequency of the VCXO consisting of the 1st crystal vibrator 1a. Thus, the fluctuations in the oscillating frequency resulting from the mechanical vibration exerted to the 1st crystal vibrator 1a is cancelled and a stable oscillating frequency is obtained.