It is necessary to allocate sufficient surplus resources to each service in order to maintain a service level of each service, but, as a result, many resources which are not used may be necessary.A resource allocation optimizing system performs, with respect to each of a plurality of services, a predictive judgement which is a determination of whether or not accurate prediction of a workload of the service is able to be anticipated, and controls allocation of a resource to the service on the basis of a result of the predictive judgement. With respect to each service, the predictive judgement is performed on the basis of at least one of (x) time-series measured workloads and time-series predicted workloads in a predefined period for the service and (y) at least one of a measured service level and a predicted service level in the predefined period for the service.