PURPOSE: To make easy the check for short circuit of disconnection of a transmission line, by applying a signal with a specified frequency from an oscillator by taking the transmission line from the output side of an amplifier to the speaker as a load, and detecting the change is the signal, in a speaker device in which the transmission line from the audio amplifier to the speaker is long.

CONSTITUTION: An output of an audio circuit 1 is applied to contacts 4a, 4c of a switch 4, and contacts 4e, 4f are connected to the primary side 3a of an anti-lighting transformer 3. Contacts 4b, 4d are connected to connection terminals 20, 21 of a speaker operation detecting circuit 10, and an output of an oscillator 11 of the circuit 10 is applied to terminals 22 and 23. A voltage detection circuit 12 is connected between a mutual connecting point (a) with terminals 20, 22 and a mutual connecting point (b) with the terminal 23 and a current detection circuit 13 to detect a load voltage. Thus, the transmission line from the terminals 20, 21 to a speaker 8 is taken as a load of an oscillator 11, allowing to detect the increase in the load impedance due to disconnection as a voltage change at the terminals 22, 23 and a current change at the terminals 21 and 23.