PURPOSE: To give the caches of files to respective systems for improving write performance being the weak point of a conventional network file system.

CONSTITUTION: In a network file system which can virtually access the file of a computer constituted on a network, a client management means 21, a request forward means 22 and a request reply means 23 constitute an illustrated computer system 2. A file cache means 11, a request reply means 12 and a cache flash means 13 constitute a computer system 1. In the network file system, write performance is improved by giving the file cache to a client at the time of write.