In a circuit for preventing breakdown of a load resulting from a wrong connection of a power source, there are provided a first load to which a DC voltage source should be applied at a predetermined polarity and to which a wrong polarity connection of the DC voltage source should be prevented, a second load to which the DC voltage should be applied, and a transistor having the base thereof connected to the second load and the collector thereof connected to one terminal for connection with the DC voltage source. The first load is connected between the base electrode and emitter electrode of the transistor. The junction of the first and second loads is connected to another terminal for connection to the DC voltage source.