1. A server system comprising: a plurality of physical servers on which a plurality of virtual servers run; and a management device which is connected through a communication network to said plurality of physical servers and manages said virtual servers running on said physical servers, said management device comprising: a judging unit that divides a process of judging whether or not an available resource capacity, in a case where said virtual servers run on said physical servers, satisfies a predetermined condition, into plural processes for every predetermined unit of time, and performs said processes of judging through parallel distributed processing.