Confidential information leakage prevention system, confidential information leakage prevention method and confidential information leakage prevention program

A system is configured such that two or more clients each having an application program that transmits a network access request and a server can communicate with each other. At least one client comprises a first control means for controlling the access request to the server on the basis of the security level assigned to the application, and the server comprises a second control means for determining whether the first control means is installed in the client which has transmitted the access request, permits the access request when the result of the determination is yes, and controlling the access request on the basis of the security level assigned to an object to be accessed when the result of the determination is no.