Memory rewriting system for vehicle controller

A memory rewriting system for a vehicle controller is provided. The system comprises a vehicle controller 10 and an external rewriting device 11. A vehicle controller comprises a rewritable memory 16 storing first security data. The first security data is used to determine whether rewriting to the rewritable memory is permitted. The rewriting device transfers new security data to the vehicle controller. The vehicle controller deletes the first security data and writes the new security data into the rewritable memory. Rewriting the new security data is performed by a program-stored in a non-rewritable memory 18. Thus, the security data that is used to determine whether rewriting to the rewitable memory is permitted is rewritten with the new security data. Therefore, if the existing security data stored in the vehicle controller is invalidated, the security feature of the vehicle can be recovered. The vehicle may include an anti-theft system 81. In this case, rewriting to the rewritable memory is permitted if the anti-theft system permits an operation as to the vehicle.