Physical quantity sensor

A physical quantity sensor comprises a driving circuit that drives a sensor element based on a reference signal; the sensor element that is driven by the driving circuit to convert an externally applied physical quantity to an electrical signal; and an amplifier circuit that amplifies an output signal of the sensor element . The driving circuit controls a driving signal, which drives the sensor element, based on the reference signal so that the driving signal is at a fixed level, and the amplifier circuit has a gain characteristic that amplifies the output signal in a direction reverse to a direction in which the reference signal varies or the driving signal of the driving circuit varies. This configuration allows the physical quantity sensor to reduce output level variations in the sensor output against signal level variations in the reference signal and to make the sensitivity constant.