A file server holding tag information representative of file contents and an access frequency of each file calculates a tag rating from the access frequency of each file and calculates a file rating from the tag rating affixed to the file. It controls to place a file having a high calculated file rating on a higher transfer performance layer, and place a file having a low calculated file rating on a lower transfer performance layer. Rapid accesses can be handled quickly by placing in advance a file whose access is anticipated to be increased after interest is increased although an access frequency is still low, on a layer having a short response time and high throughput, and by maintaining a file whose access is anticipated to be increased because of increased interest although an access frequency is lowered, on a layer having a short response time and high throughput.