The invention provides a microphone amplifier circuit which enhances the SNR (signal noise ratio) and expands the dynamic range by reducing the noise level. A microphone amplifier circuit includes a preamplifier which amplifies an audio signal from a capacitor microphone, a level detection circuit which outputs a level detection signal when the level of the audio signal is in the vicinity of the noise level of the microphone amplifier circuit, and an attenuator which attenuates the level of the audio signal outputted from the preamplifier in response to the level detection signal. The preamplifier includes an operational amplifier, a feedback capacitor and a feedback resistor.