1. An electronic apparatus comprising: a rewritable nonvolatile memory that memorizes a plurality of programs including a start processing program needed for a start processing, an executive operation program needed for an executive operation of a function, and header information for information about the start processing programs and the executive operation program; a volatile memory that memorizes a plurality of programs for updating; and a processor that memorizes the plurality of programs in the volatile memory, writes the plurality of programs for updating in the nonvolatile memory, and when writing the plurality of programs for updating in the nonvolatile memory, writes the start processing program for updating beforehand in a state of being reserved the start processing program and the header information before updating, writes the header information for updating subsequently, and writes the executive operation program for updating after that.