To extremely shorten the time up to detection of an access concentration by enabling the grasping of the tendency of starting the access concentration to a specified content.

An access detection function 11 detects accesses to each content and transmits them to a database. An access history database 12 stores the transmitted data and transmits necessary information according to a request from an access concentration determination function 13. The access concentration determination function 13 sets a measuring interval of 10 seconds based on the data transmitted from the database 12 and measures the access number to each content at every measuring time. A content which has five largest access numbers in a row is determined as an access-concentration content. The name of the determined content is outputted from an external output function 14. When the access-concentration content is detected, this content is mirrored to a cache server.