An acceleration sensor, including: an oscillator unit for outputting an oscillator signal, the oscillator unit including a first piezoelectric vibrating reed having a vibrating arm that performs bending vibration, as well as an oscillator circuit for oscillating the first piezoelectric vibrating reed; a phase shifting unit for shifting and outputting a given phase angle of an output signal of the oscillator unit; a phase shift circuit unit provided with a second piezoelectric vibrating reed having a vibrating arm that performs bending vibration, arranged at an output side of the phase shifting unit; a multiplier for multiplying the output signal of the phase shift circuit unit by the output signal of the oscillator circuit; and a phase shift modification output unit which receives an output from the multiplier and outputs a value corresponding to a change in a phase shift angle of an input-output signal of the phase shift circuit unit; a resonant frequency of the second piezoelectric vibrating reed being equal to a frequency of the output signal of the oscillator unit, in a state where no acceleration is applied.