To provide an acceleration sensor dispensing with any angle sensor, needing only one weight, having a compact and simple structure dispensing with any rotation mechanism, reducing a manufacturing cost, having good responsiveness, and properly sensing acceleration even if it is somewhat inclined in a direction not supposed in ordinary use.

This acceleration sensor, housed in a case and mounted on an object of measurement whose acceleration is to be measured, is equipped with a gravity-directional component extraction part for extracting a gravity- directional component of acceleration undergone by the object and a piezoelectric element for generating a voltage by being deformed by the directional component of the acceleration.