PURPOSE: To obtain plural frequencies from one crystal resonator in use by providing plural amplifiers designed to satisfy the oscillating condition at each resonance point of the crystal resonator and a switch circuit selecting them to the oscillator so as to select an amplifier thereby selectively outputting any of the plural oscillating frequencies.

CONSTITUTION: An amplifier AMP1 is designed to satisfy the oscillating condition of a primary resonance frequency being a multiple of one of a frequency of the fundamental wave mode, an amplifier AMP2 is designed to satisfy the oscillating condition of a ternary resonance frequency being a multiple of three of a frequency of the fundamental wave mode, and an amplifier AMP3 is designed to satisfy the oscillating condition of a quinary resonance frequency being a multiple of five of a frequency of the fundamental wave mode. When the amplifier AMP1 is selected by inputting selection signals A0, A1 to multiplexers MPX1, MPX2 respectively, the same frequency as the frequency of the fundamental wave mode of the crystal resonator X is outputted. Moreover, when the amplifier AMP2 is selected, the frequency being a multiple of three of the frequency of the fundamental wave mode of the crystal resonator X is outputted. Furthermore, when the amplifier AMP3 is selected, the frequency being a multiple of five of the frequency of the fundamental wave mode of the crystal resonator X is outputted.