1. A computer system for executing a process specified by a user and charging the user for the process, comprising: a receiving part for receiving an instruction to execute the specified process and a service level request to be satisfied by a resource which executes the specified process; a determining part for determining an external resource to provision from a first other computer system for a charge; an external resource securing part for securing the external resource on the first other computer system; an internal resource security part for securing an internal resource of the computer system; and an executing part for causing the external resource to execute at least a part of the specified process and the internal resource to execute the other part of the specified process, wherein: the determining part further determines whether or not to execute provisioning to replace an operating system or an application program running on at least one of the resources of the computer system with another operating system or application program, and secures the resources which satisfy the service level request and also require the minimum cost of support including the cost required for the provisioning among available resources of the computer system and the first other computer system, as the internal resource and the external resource.