PURPOSE: To obtain a sound volume adjusting circuit with a small sound of noise and a large permissible input and with high accuracy even if attenuation is large, by changing the amount of feedback and attenuation with one variable resistor in common for an audio amplifier.

CONSTITUTION: An output attenuation resistor R3 is inserted between an output side of a non-inverting amplifier 3 and an output terminal 2 and a variable resistor 4 (R4 in resistance value) grounded with a slider section is inserted between the output terminal 2 and an inverting input of the non-inverting amplifier 3. The variable resistor 4 is split into a resistor r1 part and a resistor r2 part with the sliding of the grounded slider section. The resistor r1 part is a part of a feedback resistor and the resistor r2 part is a part of an output attenuation resistor. That is, the overall gain (attenuation) G is changed by sliding the grounded slider of the variable resistor 4 for changing the ratio of the resistance values r1:r2.