Abstract: A power source device in which, even in case of mistaken connection of a source power supplying cable, the supply of source power can be halted before destruction of an electronic equipment or of the power source device itself at the time of supplying the source power. A micro-computer 8 is started when fed with the source power from a power source circuit 1, and controls a constant current circuit 2 for not impressing a load voltage across a resistor R1. A camera device 30 is fed with a dc current for load resistance detection via a resistor R2 and a diode D1. A comparator 3 sends to a port P1 of the micro-computer 8 a level signal specifying whether or not the resistance RL is higher than a pre-set value. The micro-computer 8 controls the constant current circuit 2 for supplying the source power to the camera device 30 if the level signal supplied to the port 1 is `1`, that is if the load resistance RL is higher than a pre-set value.