A decompression and restoration unit, when differential data between a new execution program and a specific program is input, decompresses and restores the compressed specific program and rewrites the execution program as the specific program. A differential restoration unit differentially restores the new execution program from the differential data and the specific program and rewrites the specific program as the new execution program. A differential restoration unit that, when differential data between a new execution program and a specific program is input, differentially restores the new execution program from the differential data and the execution program in a memory unit and rewrites the execution program in the memory unit as the new execution program. The decompression and restoration unit decompresses and restores the compressed specific program and rewrites the new execution program as the specific program.