1. A resource assignment manager that determines computers on which an application is newly executed out of pooled computers, adopted in a system in which each of a plurality of applications is executed on at least one of a plurality of computers and requests to an application are distributed to and processed by computers on which said application is executed, comprising: a resource information storage means, which stores specification information of each computer; a processing capacity storage means, which stores, for each of said plurality of applications, correspondence between specification information of a computer and a number of processed requests per unit of time, said number being expected if the application in question is executed on a computer having said specification information; a required resource amount estimation means, which specifies, for each of said plurality of applications, an application deficient in resources based on a difference between a number of received requests per unit of time and a number of processed requests per unit of time in each of computers assigned to the application in question, and calculates said difference in number of requests as a required resource amount for said application specified as one deficient in resources; and a configuration change means, which determines computers required for processing the required resource amount estimated by said required resource amount estimation means, out of said pooled computers, based on the specification information, stored in said resource information storage means, of each of said pooled computers, the specification information of a computer stored in said processing capacity storage means, and the correspondence between the specification information of the computer and the number of processed requests per unit of time, said number being expected if the specified application deficient in resources is executed on the computer having said specification information.