An acceleration sensor includes: a piezoelectric vibration device; an oscillation circuit; and a detection circuit, wherein the piezoelectric vibration device includes a substrate, an insulation layer formed above the substrate, a vibration section forming layer formed above the insulation layer, a vibration section formed in a cantilever shape in a first opening section that penetrates the vibration section forming layer, a second opening section that penetrates the insulation layer and formed below the first opening section and the vibration section, and a piezoelectric element section formed on the vibration section, the oscillation circuit vibrates the piezoelectric vibration device at a resonance frequency, and the detection circuit detects a change in the frequency of vibration of the piezoelectric vibration device which is caused by an acceleration applied in a direction in which the vibration section extends, and outputs a signal corresponding to the acceleration based on the change in the frequency.