To change configuration of previous data according to new configuration information of data when program of an electronic control device is changed.

The electronic control device is provided with a rewritable first nonvolatile memory for storing computer program and a rewritable second nonvolatile memory for storing data which is used by the program. The electronic control device includes a means for writing computer program on the first nonvolatile memory with connected to an external device. The electronic control device includes a means comparing the configuration of data stored in the second nonvolatile memory and data configuration information specified by the program stored in the first nonvolatile memory, converting data stored in the second nonvolatile memory to a new configuration according to the first configuration information and writing the same on the second nonvolatile memory.