To provide a fixed voltage power source circuit having a protecting circuit capable of a stable protecting operation even at reducing a power to be consumed by a protecting circuit.

When output currents io reach a predetermined current value or more, and a protecting circuit part 3 starts to operate, a switch circuit SW1 is turned on into a conductive state by a comparator C1 so that a power can be supplied to an arithmetic amplifier A2 of the protecting circuit part 3. When the output currents io are a predetermined current value or less, the switch circuit SW1 is turned off into a disconnected state by the comparator C1 so that power supply to the arithmetic amplifier A2 of the protecting circuit part 3 can be stopped.