To prevent an output transistor from thermal breakdown due to an overcurrent caused by an output short circuit of a class D audio amplifier.

The amplifier output circuit comprises protection control circuits 11, 12, 21, 22 which detect potential differences i.e., voltages between the sources and the drains of output transistors Tr11, Tr12, Tr21, Tr22, compare the detected voltages with a specified voltage and, if the detected voltage exceeds the specified voltage, output a short circuit detect signal to the gates of the output transistors Tr11, Tr12, Tr21, Tr22, thereby turning off the output transistors Tr11, Tr12, Tr21, Tr22.