In a system including a load balancer to select a virtual server to which a request is to be transferred, the load balancer includes a function to monitor resource use states of physical and virtual servers and a function to predict a packet loss occurring in a virtual switch. The request count of requests processible by each virtual server is calculated based on the resource amount available for the virtual server and a packet loss rate of the virtual switch, to thereby select a virtual server capable of processing a larger number of requests.