PURPOSE: To improve the distortion rate and the noise characteristics, by applying an input voltage to the input terminal of a negative feedback amplifier and taking out a current corresponding to this input voltage as the sum of currents flowed to positive and negative power supply terminals of this amplifier.

CONSTITUTION: The sum of currents (i5+i7) flowed to positive and negative power supply terminals of a negative feedback amplifier 8 is equal to a current i6 flowed to a resistance R5. Since voltages generated in a noninversion input terminal NINV and an inversion input terminal INV of the negative feedback amplifier 8 are superior in distortion rate characteristics and noise characteristics by the action of the negative feedback, the current i6 flowed to the resistance R5 is superior in distortion rate characteristics and noise characteristics; and consequently, the sum of currents flowed to positive and negative power supply terminals which is equal to the current i6 is superior in distortion rate characteristics and noise characteristics.