A physical quantity sensor includes a sensor element that converts an externally applied physical quantity to an electrical signal; a detection circuit that amplifies and detects the output signal of this sensor element; and an adjustment circuit that adjusts the output signal from the detection circuit to a predetermined signal by applying the power supply wherein the adjustment circuit comprises an amplifier circuit that amplifies the output signal from the detection circuit and a reference amplifier circuit that has a gain that is made to correspond to the gain of the amplifier circuit. This configuration allows the gain of the amplifier circuit in the adjustment circuit to be varied according to the power supply voltage and, as a results, provides a physical quantity sensor having reliable sensor detection sensitivity and high-accuracy ratiometric characteristics.