An electronic control unit includes a difference data acquisition unit that is configured to acquire difference data that is data to be written into a data storage area of the electronic control unit, the difference data being a difference between old data and new data, a consistency determination unit that is configured to determine whether the difference data is consistent with the data storage area or storage data stored in the data storage area based on first determination information related to the storage data and second determination information acquired in association with the difference data, an update data restoration unit that is configured to restore update data as the new data using the difference data and the storage data when the consistency determination unit determines that the difference data is consistent, and a data writing unit that is configured to write the update data restored by the update data restoration unit into the data storage area.