The invention provides an amplifier circuit of a capacitor microphone of which the noise resistance against noise of a supply voltage is enhanced. In an amplifier circuit of a capacitor microphone of the invention, while a noise component of a supply voltage is applied to one inversion input terminal of an operational amplifier of an amplification portion through a parasitic capacitor existing between an external power supply wiring and an external wiring that are adjacent to each other, the problem noise component of the supply voltage is applied to the other non-inversion input terminal by capacitive coupling to an internal power supply wiring. Therefore, the noise component is cancelled at the operational amplifier.