An amplifier circuit includes first and second amplification units. A first detection electrode and a high impedance circuit are connected to the input terminal of the first amplification unit. A second detection electrode and a high impedance circuit are connected to the input terminal of the second amplification unit. The output terminals of the first and second amplification units output first and second output signals, and are connected to the input terminals of a differential amplifier circuit through coupling capacitors, respectively. The differential amplifier circuit operates a difference between the first and second output signals in a state where a direct-current component is omitted.