PURPOSE: To limit an output current without decreasing a maximum output voltage by detecting an emitter-base voltage of an output transistor(TR), outputting a current proportional to the voltage and controlling the base drive current of the output TR in response to the output current.

CONSTITUTION: A base and an emitter of NPN TRs 29, 30 are connected respectively to a base and an emitter of output TRs 17, 18. The emitter area ratio of the TRs 17, 18 and 29, 30 is set to be 1000:1. When the collector current of the output TR 17 is increased, the collector current of the TR 29 is increased by the same ratio only. Then a current proportional to the current flows to a current sensing resistor 23 via a current mirror circuit 33 and the voltage across the resistor 23 exceeds a base-emitter voltage of the TR 24, then the TR 24 starts turning on and the base current of the TR 19 is decreased, Then the base current of the output TR 17 is decreased and the increase in the collector current is suppressed. The operation is similar to the output TR 18.