PURPOSE: To cache more data in a cache area of the same capacity by providing a cache control means which constantly holds a cache and a control means which compresses the cache contents

CONSTITUTION: When an access request is accepted, a CPU 10 obtains a cache entry list 44 by referring to the header part 30 of a permanent cache file. The CPU 10 searches the cache entry list 44 to decide whether or not there is data to be accessed in the cache. When the target data is present in a cache file, a cache entry 46 is obtained and the compressed data of the corresponding block are obtained by referring to the cache contents list. Then a compression/ expansion controller 16 expands the block and sends the data to the network node which has sent the request. Data which are hit at the time of caching are reused with high probability, so the order of the object of deletion in the cache entry list 44 is lowered.