A packet priority level is set for a packet configuring a file access request, and a file importance level is set for a file. A storage controller manages, for each client, the amount of information (total amount) in the packets sent and received for each packet priority level, and the amount of information (total amount) in the access-targeted files for each file importance level. The storage controller computes an assessment value for assessing whether a target client is appropriate or inappropriate based on one or more amounts of information corresponding to the target client and one or more packet priority levels, and one or more amounts of information corresponding to one or more file importance levels respectively corresponding to one or more packet priority levels and the target client, and determines whether the target client is appropriate or inappropriate in accordance with whether or not the computed assessment value conforms to a prescribed condition.