A firmware update system updating old firmware in an information apparatus to new firmware, comprising: a management apparatus generating firmware update data; and an information apparatus acquiring the firmware update data and updating the old firmware to the new firmware, wherein the management apparatus generates difference data from data of the old firmware and the new firmware, generates an update procedure document describing an update process for generating the new firmware from the old firmware and the difference data in the information apparatus, generates writing back reference information describing information for performing a writing back process of recovering data in an update process in the information apparatus to a state before starting of the update process when the update process has been interrupted, and generates the difference data, the update procedure document and the writing back reference information as the firmware update data, and the information apparatus updates the old firmware to the new firmware on the basis of the difference data, the update procedure document and the writing back reference information included in the firmware update data; wherein the management apparatus divides the old firmware and the new firmware into a plurality of blocks, processes the blocks in units of blocks, and generates the firmware update data; characterized in that the management apparatus provides a plurality of processing orders for performing an update process on the plurality of blocks, generates intermediate data representing a status of each block in rewriting from the old firmware to the new firmware with respect to each processing order, and checks necessity of backup and necessity of extracting difference data in the units of blocks using the new firmware and the intermediate data, and identifies the processing order whose total value of a capacity required for the backup and a capacity required for storing the difference data among the plurality of processing orders on the basis of a check result pertaining to the necessity of backup and the necessity of extracting the difference data is the smallest, and describes the identified processing order in the update procedure document. a management apparatus generating firmware update data; and an information apparatus acquiring the firmware update data and updating the old firmware to the new firmware, wherein the management apparatus generates difference data from data of the old firmware and the new firmware, generates an update procedure document describing an update process for generating the new firmware from the old firmware and the difference data in the information apparatus, generates writing back reference information describing information for performing a writing back process of recovering data in an update process in the information apparatus to a state before starting of the update process when the update process has been interrupted, and generates the difference data, the update procedure document and the writing back reference information as the firmware update data, and the information apparatus updates the old firmware to the new firmware on the basis of the difference data, the update procedure document and the writing back reference information included in the firmware update data; wherein the management apparatus divides the old firmware and the new firmware into a plurality of blocks, processes the blocks in units of blocks, and generates the firmware update data; characterized in that the management apparatus provides a plurality of processing orders for performing an update process on the plurality of blocks, generates intermediate data representing a status of each block in rewriting from the old firmware to the new firmware with respect to each processing order, and checks necessity of backup and necessity of extracting difference data in the units of blocks using the new firmware and the intermediate data, and identifies the processing order whose total value of a capacity required for the backup and a capacity required for storing the difference data among the plurality of processing orders on the basis of a check result pertaining to the necessity of backup and the necessity of extracting the difference data is the smallest, and describes the identified processing order in the update procedure document.