A physical quantity sensor comprises a sensor circuit that converts an externally applied physical quantity to an electrical signal and outputs a detection signal; an adjustment circuit that adjusts the detection signal, which is received from the sensor circuit, to a predetermined signal; and an output circuit that forms an output signal from the signal of the adjustment circuit wherein the sensor circuit and the output circuit are driven by a common power supply voltage. The adjustment circuit comprises a pulse generation circuit that generates a pulse modulation signal based on the power supply voltage; and an amplifier circuit that amplifies the detection signal, which is received from the sensor circuit, with a gain made variable by the pulse modulation signal, wherein the detection sensitivity of the output signal is made variable according to the power supply voltage. This configuration enables the amplifier circuit, provided in the adjustment circuit, to output a sensor output that has high linearity characteristics and, as a result, implements a physical quantity sensor with highly accurate sensor detection sensitivity and allows the physical quantity sensor to have good detection-sensitivity ratiometrics characteristics, high linearity, and desired-characteristic detection sensitivity.