An electronic control unit comprises a central processing unit for calculating plural types of control data used for controlling a control object and a non-volatile memory rewritable of data. The processing unit writes sequentially type-affixed control data, in each of which type information indicating a type of control data is affixed to the control data, into a data write-in area in the non-volatile memory. When a hold condition corresponding to one of the plural types of control data is satisfied, the processing unit reads out the type-affixed control data, which includes the control data corresponding to a satisfied hold condition, from the data write-in area based on the type information, and writes the type-affixed control data read out from the data write-in area in a data holding area of the non-volatile memory.