An amplifier circuit converts a charge signal into a voltage signal. The charge signal indicates a detection result outputted from a piezoelectric device that detects a detection object as a change in an amount of a charge. The charge signal includes a displacement signal in a predetermined frequency band. The amplifier circuit includes an operational amplifier including an inverting input terminal receiving the charge signal and an output terminal for outputting the voltage signal, a resistor electrically connected between the inverting input terminal and the output terminal, and a capacitor connected in parallel with the resistor. A resistance value of the resistor and a capacitance value of the capacitor are set such that, in the frequency band of the displacement signal, an absolute value of an impedance of the resistor is lower than an absolute value of an impedance of the capacitor.
