To protect an in-device circuit so as not to interfere with an audio amplifier use by a user.

A protection control circuit 15 makes an input limitation circuit 12 perform attenuation processing of a voice signal, when a current detected by a current detecting portion 17 and a temperature detected by a temperature detecting portion 16 have reached a level requiring a circuit protecting operation. In the attenuation processing, the input limitation circuit 12 outputs the voice signal inputted to an amplifying circuit 13, without attenuating a middle frequency area. For low and high frequencies, in which human aural sensitivity is low, the lower the frequency is, the greater the frequency is attenuated in the low frequency side, the higher the frequency is, the greater the frequency is attenuated in the high frequency side, and the voice signal is outputted to the amplifying circuit 13.