Electronic Control Device

Even when a power supply relay cannot be turned off and when power supply to a microcomputer is normally cut off, fixing of the power supply relay is detected. An electronic control device according to an aspect of the present invention includes a relay drive circuit that controls on and off of a power supply relay according to information about the on and off of power supply, an electronic circuit (first power supply system block , microcomputer ) that operates at a first power supply voltage (V) supplied from a battery through the power supply relay , and a monitoring unit (second power supply system block ) that monitors the first power supply voltage when the power supply is turned off, and holds a monitoring result, the first power supply voltage reflecting presence or absence of fixing of the power supply relay.