To provide an acceleration sensor which is simplified in formation, and can be extremely easily designed and manufactured, and moreover can accurately detect acceleration.

An acceleration sensor is provided with a displacement detecting section 7 to output the two values of detecting outputs according to a side where a pendulum 2 to move in response with acceleration is positioned to a reference position, and a driving means 4 for driving the pendulum 2 in the direction for returning the pendulum 2 toward the reference position according to the detecting output generated by the displacement detecting section 7, and the acceleration is detected on the duration time of any direction where driving power is given to the pendulum 2 by the driving means 4.