A reverse polarity protection circuit includes a p-channel MOSFET, an n-channel MOSFET, zener diodes, a coil that suppresses a backward flow of an electric current, a resistor that retains a voltage difference between a source of the p-channel MOSFET and a drain of the n-channel MOSFET, a resistor that protects the circuit if short-circuit destruction of the p-channel MOSFET occurs, a resistor that protects the circuit if short-circuit destruction of the n-channel MOSFET occurs, an electrolytic capacitor that suppresses fluctuation in an input voltage to a power supply control IC, a battery that supplies a voltage to an ECU, and the power supply control IC that generates a voltage for causing an IC in the ECU to operate.