The present invention provides a method of easily managing two or more OSs. A host OS, a guest OS, and a virtualization module are loaded into a primary physical address area of a main memory. The guest OS is executed in a virtual environment in a primary physical address area. A memory image of the guest OS loaded in the primary physical address area is copied to a secondary physical address area. The right of access to a processor is transferred to the guest OS copied in the secondary physical address area to execute the guest OS in a physical environment.