The on-vehicle electronic control device includes a main power supply circuit fed with power from an on-vehicle battery through an output contact of a power supply relay and a main power supply terminal of a connector to supply a stabilized control voltage to a microprocessor. When contact failure occurs in the main power supply terminal, the main power supply circuit is fed with bypass power from the output contact through a first electrical load and a commutation diode to perform the one of the report of the abnormality and the storage of the abnormality occurrence history information. A bypass power fed state is detected when an input voltage to the main power supply circuit is lower than a power supply voltage of the on-vehicle battery.