Provided is a computer system, including: at least one storage system providing at least one logical volume, at least one host computer including an I/O device, and a management computer, in which the management computer creates a virtual computer within a network segment to which the management computer belongs, the virtual computer including an I/O device that is the same as the I/O device of the host computer in number and type, defines a connection between the logical volume and the virtual computer, stores a program in the logical volume connected to the virtual computer, sets identification information on the host computer in the virtual computer, releases the connection between the logical volume that stores the program and the virtual computer, and defines a connection between the logical volume whose connection has been released and the host computer.