To prevent improper rewriting of control information in an electronic controller even if a rewriting device or the information inside the rewriting device is stolen.

The rewriting device 20 stores a function(f) required for the access to ECUs 11 to 14 in a center 30. The center 30 sends the function(f) to the rewriting device 20 for the first time after judging that the rewriting device 20 is a proper one. The center 30 has the database stored by corresponding ID information allocated uniquely to the rewriting device 20 to telephone number on the rewriting device 20 side when data communication is done through a telephone network 40. In obtains the ID information from the rewriting device 20 and the telephone number of the origin of call to judge that the rewriting device 20 is the proper one when the corresponding relation between this ID and the telephone number coincides with the corresponding relation stored in the data base.