Abstract: An electronic control device comprises a reverse connection protection relay, a voltage detector, and a control device. The reverse connection protection relay comprises a switching element and a rectifying element. The switching element and the rectifying element are connected in parallel. A negative electrode of the rectifying element and a positive electrode of the rectifying element are connected to a negative electrode of a power source and a load, respectively, the load consuming power supplied from the power source. Opening and closing of the switching element are controlled on the basis of a switching control signal indicating presence or absence of power supply from the power source. The voltage detector is configured to detect a potential difference between both ends of the reverse connection protection relay. The control device is configured to determine a state of the reverse connection protection relay on the basis of the potential difference.