For each of multiple migration policies, a server system 2 that accesses a storage apparatus 10 obtains a resource use amount needed to execute the migration. Each of the migration policies includes information for specifying a resource use amount of the server system 2 needed to execute the migration according to the policy. Then, the server system 2 allocates an amount of usable resources to each of the policies in accordance with the resource use amount obtained for the policy; in the migration according to each of the policies, allocates a certain amount of resources usable for executing the migration, to the virtual server which serves as either of a migration destination and a migration source, while determining the certain amount of resources within the amount of resources allocated to the policy; and executes the migration according to each of the policies in accordance with the resource use amount allocated to the policy.