PURPOSE:To improve the voltage reduction characteristics and then prevent the excessive flip-flop output when the power source is applied, by installing the muting circuit at the input part of a power amplifying circuit and then securing an automatic working for the muting circuit in the state which is required for the operation of the first-stage amplifier. CONSTITUTION:The collector output (opposite phase signal V1) of the transistor Q4 of the first- stage phase dividing circuit 13 is applied to the base of Q16 of the differential amplifier consisting of the complementary transistors Q16 and Q17 having the common emitter. The intermediate voltage VQ of the output-stage amplifier 1 is applied to the base of Q17 via the negative feedback circuits R14, R15 and C'' each. The power source voltage of the circuit 13 is obtained from the emitter of the voltage dividing output Q3. The constant current is obtained via the base-emitter voltage of the constant voltage Q12 and then flowed to the current Miller circuits (Q14 and Q15) via R13 to be supplied to the amplifier 1. The constant current load I0 is provided to the collector of Q16 and then supplied to the amplifier 1. At the same time, the forward phase output V2 is obtained from the collector of Q3 to pass through the intermediate- and output-stage amplifiers 2' and 1' each. And the differential voltage between the outputs 1 and 2 is used to drive the load SP, and thus the output fluctuation is negated in the same phase.