oscillation may occur by a high frequency signal of for example 1 mhz the power amplifier 13 of course delivers a high frequency signal of a high level and the voltage responsive to this high level is applied to the base of the transistor 23 as a result the transistor 23 is made on and hence the potential at the input terminal 18 of the control and drive circuit 16 becomes for example 1 v as described previously then the drive transistor 35 in the control and drive circuit 16 turns to off from on accordingly the excitation of the relay coil 17 is stopped as a result the relay contact x 1 which is opened up to now is closed and hence the power amplifier 13 becomes inoperative at the same time the relay contact x 2 is opened to stop the power supply to the speaker by the manner set forth above upon the generation of high frequency oscillation the power amplifier 13 and speaker can be prevented from being damaged as described above according to the protective circuit for the power amplifier of the present invention a high frequency signal exceeding the audio frequency range is detected by the high frequency signal detector 15 the control and drive circuit 16 stops the power supply to the relay coil 17 based upon the detected output and hence the power amplifier 13 is made inoperative thus the power amplifier 13 can be avoided.