To provide a control device that can store information required for analyzing a failure upon occurrence of the failure without damaging such information and can reduce the capacity of data to be stored in a memory, compared to a conventional technology.

An arithmetic unit 20 temporarily stores specific vehicle condition data in a volatile memory 22 when a vehicle failure is detected. An optimal layer is alternately determined by a plurality of pieces of vehicle condition data entered in the arithmetic unit 20 from a map 24 which is preliminarily classified to each layer and stored in a ROM, and the management code allocated to the determined layer is stored in a nonvolatile memory 30.