1. A file management program which makes a computer perform processing for management of files in a storage device, comprising: a hash-value generation unit which receives a processing request containing name information for a file to be processed, applies a predetermined hash function to the name information, and generates a hash value of the file to be processed; a physical-block-number acquisition unit which looks up a hash-value-range table containing at least one hash-value-range information set each of which is constituted by a hash-value range defining a range of hash values and a physical-block number uniquely indicating a data storage region in said storage device, extracts one of the at least one hash-value-range information set in which a hash-value range containing the hash value of the file to be processed is included, and acquires a physical-block number from the one of the at least one hash-value-range information set; and a directory processing unit which performs processing of a physical block in said storage device corresponding to said physical-block number acquired by said physical-block-number acquisition unit, where the processing relates to a record containing said name information and is performed in accordance with said processing request.