1. A server system comprising: a plurality of physical servers, each of said plurality of physical servers making a plurality of virtual servers run or operate thereon; 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 performs a judging process of judging whether or not an available resource capacity satisfies a predetermined condition, in a case where said virtual servers run on said physical servers; and a collection unit that collects, every collection time in a predetermined time span, through said communication network, plural sets of load data concerning said plurality of virtual servers and said plurality of physical servers, said plurality of virtual servers and said plurality of physical servers performing at least a predetermined process, and said load data of said plurality of physical servers and said plurality of virtual servers having a load peak which periodically appears every said predetermined time span, when said plurality of virtual servers and said plurality of physical servers perform said predetermined process, said time span being divided into a plurality of predetermined units of time, said load data in said time span being divided into a plurality of data sets respectively corresponding to said units of time, wherein said judging unit of said management device has a plurality of processing units, the processing units respectively performing said judging processes on the data sets of said load data of the physical servers and virtual servers respectively corresponding to said units of time, each of said processing units performing said judging process on a whole of a plurality of data sets of said load data collected from said plurality of physical servers at same collection times within a unit of time, said processing units preforming said judging processes in parallel, thereby performing a plurality of said judging processes through parallel distributed processing.