Switching of the allocation of a device to a guest OS is implemented through transmission of a virtual suspension interrupt to a guest OS in a VMM; a power control notification process module that causes the guest OS to start a return process from a suspended state; a guest power process module that traps a suspension process of the guest OS; an I/O configuration change process module that updates a logical device definition of the VMM in the suspended state of the guest OS; a guest I/O emulation process module that emulates an I/O instruction that is issued by an I/O reconfiguration process module and that is executed when the guest OS has returned from the suspended state, thereby to provide a new logical device configuration to the guest OS.