By automatically adjusting a gain according to the presence or absence of head set connection and a head set microphone, an electronic circuit has improved sound collecting performance and prevents the microphone from casually collecting sound. In the circuit, a voltage detecting unit (105) outputs a result of comparison between power voltage and a threshold value or a digital value of the power voltage. A control unit (106) detects the presence or absence of a head set microphone (161) based on the comparison result or the digital value of the power voltage in the voltage detecting unit (105). A gain setting unit (109) sets a gain of a value larger than that in the case where the absence of the head set connection is detected by the control unit (106), when the presence of the head set connection and the absence of the head set microphone are detected by the control unit (106). A variable amplifier (110) amplifies audio data from a body microphone (107) using the gain set by the gain setting unit (109).