An acceleration sensor includes first and second opposed electrode units. The first opposed electrode unit includes a first electrode and a second electrode spaced away from and facing the first electrode, and provides a first capacitance. The second opposed electrode unit includes a third electrode and a fourth electrode spaced away from and facing the third electrode, and provides a second capacitance. The first and third electrodes are arranged along a first direction. A component of acceleration along the first direction applied to the object is detected based on the first and second capacitances. A control voltage is applied to the first and second opposed electrode units. The control voltage is changed when both of the first capacitance and the second capacitance simultaneously increase or decrease. This acceleration sensor detects the acceleration accurately.