PURPOSE: To obtain such a reverse connection preventive circuit that a reverse voltage is not applied to a load by providing an electromagnetic connector between DC power and load, connecting a coil connected to a diode in series to a DC power side in parallel against the load, and switching and driving the electromagnetic connector with the coil.

CONSTITUTION: When the plus terminal (+) of DC power is connected to a power side terminal A and the minus terminal (-) of DC power is connected to a terminal B, the current (i) excites a coil 6 through a forward diode 5, and an electromagnetic connector 3 is closed to supply DC power to the load 2. While, in case the (-) of DC power is connected to the power terminal A and the (+) of DC power is connected to the power terminal B, the diode 5 is a backward one, the coil 6 is not excited, the electromagnetic switch 3 is opened, and DC power with reversed polarity is not supplied to the load 2. If the polarity of the power is reconnected, the electromagnetic switch is closed again, so that a reverse voltage is never applied to the load 2.