An electronic control apparatus includes a control circuit and has a power supply holding function whereby when a power switch-off command is received by the apparatus, the supplying of power to the control circuit is continued until it has completed specific processing, during a power supply holding interval. The duration of each such interval is measured and stored in non-volatile memory, and subsequently used for detecting any power supply holding function abnormality, and for ensuring that the specific processing is actually performed, and distinguishing between an abnormality causing premature switch-off and an abnormality causing failure to terminate the supplying of power.