To provide an automobile control unit that enables shorter rewriting of control software loaded on a nonvolatile memory.

A component search means searches the nonvolatile memory 5 for an update target component 10D according to the storage contents of a component management information storage means. A rewrite unit block copying means reads out the storage contents of a rewrite unit block 15 to which the target component 10D found belongs from the nonvolatile memory 5, and copies them in a rewrite buffer area 21 on a RAM 4. A component update means updates the target component 10D for changing, addition, deletion or a combination of two or more of these in the copied storage contents of the rewrite unit block 15. A nonvolatile memory write-back means writes the updated storage contents of the rewrite unit block 15 back from the rewrite buffer area 21 to the nonvolatile memory 5.

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