When a management screen for conducting management operation of a file system in the NAS apparatus 10 of a file server is displayed by the administrator on a display device of the management console 30 by using the management console 30, if a disk device obtained from the storage apparatus 20 is in a power saving state, the NAS apparatus 10 has a function to change the operations hereafter. Specifically, a screen is displayed on the management screen, in which a creation or deletion of the file system becomes impossible with respect to the disk device in the power saving state. Therefore, the administrator can conduct management operations for services without referring to the power status, thereby resulting in easy management operation.