PURPOSE: To improve distrotion and frequency characteristics in an actual in-use state by detecting and feeding positively a load current back so that the output impeance of a power amplifier and the impedance of an output cord are equalized to zero equivalently.

CONSTITUTION: The inverted input terminal of inverting amplifiers AP and AN that positive feedback circuits βP and βN are connected to the emitters of power transistors (TR) Q1 and Q2 of the final stage part P0 of the power amplifier A, and the uninverted input terminals to an output line L, and its output terminals O1 and O2 are connected in common via resistances R1 and R2, and the middle point is connected to the inverted input terminal of the prior stage part Q0. Then, the feedback gain β of the positive feedback circuits βP and βN is so set that βP= βN=β=2Z/RE.A (where RE is the emitter resistances of the power TRs Q1 and Q2, and Z is the impedance of an output cord), eliminating a signal-source impedance ZL' viewed from the input terminal Q-Q' of a speaker SP.