Amplifying device

An amplifying device for setting input impedance at several G to several tens of G and improving an ESD withstand current rating is provided. An ECM is connected to an input terminal 21 and frequency characteristics become flat to a voice band by high input impedance of a CMOS amplifier 20 and the input impedance is set at several G to several tens of G and thereby, response time after detecting a loud voice or turning on a power source of the ECM is speeded up and desired electrical characteristics are achieved. A path for releasing a surge voltage which occurs during assembly in the outside of an IC and intrudes from the input terminal 21 to a power source terminal or an earth terminal without an influence on a signal (20 Hz to 20 kHz) of a voice band entering from the input terminal 21 can be constructed by connecting a P-channel MOS transistor 27 and an N-channel MOS transistor 28 as an ESD protective element.