1. A computer system for executing a process specified by a user and charging the user for the process, comprising: at least one processor; a receiving part configured to receive 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 configured to determine an external resource to provision from a first other computer system for a charge; an external resource securing part configured to secure the external resource on the first other computer system; an internal resource securing part configured to secure an internal resource of the computer system; and an executing part configured to cause 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 is further configured to: determine whether or not to execute provisioning to replace an operating system or an application program running on the computer system with another operating system or application program, and determine resources to secure by the external resource securing part and internal resource securing part which satisfy the service level request and also require a minimum cost of support including a 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.