A crystal oscillator includes a crystal unit and a voltage-variable capacitive element that is connected to the crystal unit in series, the crystal oscillator varying an oscillation frequency by applying a control voltage between terminals of the voltage-variable capacitive element and by varying a series equivalence capacitance at a side of the oscillator circuit when observed between terminals of the crystal unit. The crystal oscillator further includes a first resistor and a second resistor for dividing the control voltage. At least one of the first resistor and the second resistor is a temperature sensing resistor, the resistance of which changes depending on a temperature, so as to correct frequency temperature characteristics of the oscillation frequency.