1. A file management apparatus for managing one or more files stored in a storage apparatus, the file management apparatus comprising: a controller; and a memory unit that stores first management information, second management information and third management information, wherein the file management apparatus is coupled to client computers, wherein said controller provides a virtual file tree to a user via one of said client computers, wherein said first management information includes: a first classification list including a plurality of first keywords; and a second classification list including a plurality of second keywords, wherein said second management information: associates said first classification list with a first tier of a first virtual file tree provided to a first user, and associates said second classification list with a first tier of a second virtual file tree provided to a second user, wherein said third management information associates each file with one of said first keywords and one of said second keywords, wherein said controller processes to provide, to said first user via one of said client computers, using said first management information and said second management information, a first directory A whose name is a first keyword A included in said plurality of first keywords and a first directory B whose name is a first keyword B included in said plurality of first keywords, wherein said controller processes to provide, to said second user via one of said client computers, using said first management information and said second management information, a second directory A whose name is a second keyword A included in said plurality of second keywords and a second directory B whose name is a second keyword B included in said plurality of second keywords, wherein said controller, in response to a request from said first user to read a first file, searches for said first file with reference to said third management information in which said first file is associated with all of keywords which are names of directories in the path in the tiers above said first file in said first virtual tree, and wherein said controller, in response to a request from said second user to read said first file, searches for said first file with reference to said third management information in which said first file is associated with all of keywords which are names of directories in the path in the tiers above said first file in said second virtual tree.