An accelerometer having a movable electrode which is moved according to acceleration with respect to a fixed electrode disposed in opposition to the movable electrode. An output device generates an output voltage which is proportional to the acceleration by measuring a gap between the movable electrode and the fixed electrode. A pulse width modulator generates pulses, wherein a pulse width of the pulses is modulated according to the output voltage, and a feedback device feeds back an electrostatic force which is proportional to the pulse width of the pulses from the pulse modulator between the movable electrode and the fixed electrode. As the acceleration in the acceleration sensor is linearly detected, the acceleration sensor is easily adjusted.