Scale-out of a controller and application migration consider the application status, laws and rules of a scale-out destination, and a resource usage status. If an operation status exceeds a threshold value, an administrative server for a computer system of a storage system calculates a first index for each execution target, including an application, a virtual machine, or a container operating in the computer system, based on information about cost, credibility, or performance when the execution target is migrated to, and caused to operate in, another computer system, and indexing information indicating laws or rules applied to the computer system using indexes. A second index indicating, as a dimensionless quantity, the selection degree of another computer system as a migration destination of the execution target is acquired. A migration destination of the execution target is decided from among other computer systems based on the first index and/or the second index.