The object of the present invention is to provide a crystal oscillator with one IC capable of effectively responding to specifications or a frequency of an installed set, an output terminal of the oscillator 1 is connected to an input terminal of the inverter 2, an output terminal of which is connected to the first resistor 7 and one terminal of the second resistor 8, the other terminal of the first resistor 7 is connected to one terminal of the first capacitor 9 and an input terminal of the first transistor 3, the other terminal of the first capacitor 9 is connected to one terminal of the first switch 11, and the other terminal of the first switch 11 is grounded, the other terminal of the second resistor 8 is connected to one terminal of the second capacitor 10 and an input terminal of the second transistor 4, the other terminal of the second capacitor 10 is connected to one terminal of the second switch 12, and the other terminal of the second switch 12 is grounded, an output terminal of the first transistor 3 and an output terminal of the second transistor 4 are connected to the oscillation output terminal 5, and the first switch 11 and the second switch 12 are controlled by the storage device 13.