To provide an electronic control device capable of judging the reset of a clock IC generated during an ECU power source off period and an electronic control device capable of correcting time stored after generation of the reset of the clock IC to right time or time close to the right time.

A clock IC incorporated into an ECU continuously measures time from initial set time, and when an ECU power source is turned off, time stored by a processing of S270 is left as off time. When the ECU power source is turned on again, on time is read from the clock IC (S205) and if on time becomes initial set time or before, off time, on time and the reset number of times at the time are stored (S240). When a failure is generated, diagnostic information including time and the reset number of times is stored (S265). When failure data is outputted, time in diagnostic information is corrected based on present time and data stored in a processing of S240 (S310).