An oscillator includes a voltage controlled oscillator, a PLL circuit, a crystal unit and an oscillator circuit configured to generate a clock, a digital control circuit, and a clock switching unit. The digital control circuit is configured to set an oscillation parameter of the oscillator circuit, and a parameter of the PLL circuit. The clock switching unit is configured to supply an output signal of the voltage controlled oscillator to the digital control circuit as a clock signal so as to cause the digital control circuit to operate using the clock signal when powered on, and configured to supply an output signal of the oscillator circuit to the digital control circuit as a clock signal after the digital control circuit sets the oscillation parameter of the oscillator circuit. An initial voltage is supplied to the voltage controlled oscillator as a control voltage when the oscillator is powered on.