An angular velocity sensor comprising: a vibration body; a sensor electrode (234, 235) provided on the vibration body for generating a signal corresponding to an angular velocity applied to the vibration body; a driving electrode provided on the vibration body, the driving electrode having a driving signal for vibrating the vibration body input thereto; a monitor electrode provided on the vibration body for generating a signal according to vibration of the vibration body; a PLL circuit including a constant voltage source for generating a constant voltage, a timing switching unit for outputting a voltage by switching selectively between the constant voltage and a voltage corresponding to the monitor signal, and a voltage-controlled oscillator for outputting an oscillation signal having a frequency corresponding to the voltage output from the timing switching unit, and a drive circuit for supplying the driving signal to the driving electrode based on the oscillation signal output from the voltage-controlled oscillator as to vibrate the vibration body at a predetermined amplitude; a sensor circuit for outputting a signal representing the angular velocity based on the signal output from the sensor electrode (234, 235); and an amplitude determination circuit for measuring amplitude of vibration of the vibration body based on a signal output from the drive circuit, wherein, when the amplitude measured by the amplitude determination circuit is smaller than a predetermined value, the timing switching unit outputs, to the voltage-controlled oscillator, the constant voltage output from the constant voltage source, characterized in that the timing switching unit outputs a start-up mode signal when the amplitude measured by the amplitude determination circuit is smaller than the predetermined value, the start-up mode signal indicating that the angular sensor cannot detect an accurate angular velocity, and wherein the start-up mode signal is output as a redundancy added to the signal output from the sensor circuit a vibration body; a sensor electrode (234, 235) provided on the vibration body for generating a signal corresponding to an angular velocity applied to the vibration body; a driving electrode provided on the vibration body, the driving electrode having a driving signal for vibrating the vibration body input thereto; a monitor electrode provided on the vibration body for generating a signal according to vibration of the vibration body; a PLL circuit including a constant voltage source for generating a constant voltage, a timing switching unit for outputting a voltage by switching selectively between the constant voltage and a voltage corresponding to the monitor signal, and a voltage-controlled oscillator for outputting an oscillation signal having a frequency corresponding to the voltage output from the timing switching unit, and a constant voltage source for generating a constant voltage, a timing switching unit for outputting a voltage by switching selectively between the constant voltage and a voltage corresponding to the monitor signal, and a voltage-controlled oscillator for outputting an oscillation signal having a frequency corresponding to the voltage output from the timing switching unit, and a drive circuit for supplying the driving signal to the driving electrode based on the oscillation signal output from the voltage-controlled oscillator as to vibrate the vibration body at a predetermined amplitude; a sensor circuit for outputting a signal representing the angular velocity based on the signal output from the sensor electrode (234, 235); and an amplitude determination circuit for measuring amplitude of vibration of the vibration body based on a signal output from the drive circuit, wherein, when the amplitude measured by the amplitude determination circuit is smaller than a predetermined value, the timing switching unit outputs, to the voltage-controlled oscillator, the constant voltage output from the constant voltage source, characterized in that the timing switching unit outputs a start-up mode signal when the amplitude measured by the amplitude determination circuit is smaller than the predetermined value, the start-up mode signal indicating that the angular sensor cannot detect an accurate angular velocity, and wherein the start-up mode signal is output as a redundancy added to the signal output from the sensor circuit