A multi-output electric power source device has at least two channels for producing a constant voltage and a constant voltage from a single input voltage. Each channel is provided with a switching regulator in the input stages thereof and a series regulator in the next stage thereof. An over-heat detector circuit is provided in common for both channels. When the over-heating of either one of switching transistors in the channels is detected, the switching regulators turn off both switching transistors thereby to interrupt both output voltages from being supplied to an external circuit. When an over-voltage is detected, series regulators also interrupt the output voltages from being supplied to the external unit.