An electronic control apparatus includes: a plurality of processing devices each having a rewritable non-volatile memory and each executing a predetermined process in accordance with stored data that is stored in the non-volatile memory, wherein one of the processing devices extracts, from rewriting data transmitted from an external rewriting apparatus and including a plurality of individual rewriting data each corresponding to one of a plurality of dedicated address ranges, one of the individual rewriting data which corresponds to one of the dedicated address ranges that is individually allocated in advance for the one of the processing devices, and rewrites the stored data that is stored in the non-volatile memory of the one of the processing devices by using the one of the individual rewriting data.