In a computer system according to the present invention, a switch-source OS controller unit includes: a OS switch request receiver unit configured to receive an OS switch request for requesting that the switch-destination OS in a suspend status becomes the OS in the active status; a switch event notifying unit configured to notify event information to the switch-destination OS or an application on the switch-destination OS, the event information being included in the received OS switch request, and requesting the switch-destination OS or the application on the switch-destination OS to perform a process; and a switch controller unit configured to call the OS switching function, by using the event information as an argument, so that the switch-destination OS becomes the OS in the active status.