A computer is provided with a measuring unit that measures elapsed time at a non-access state between one of the guest virtual machines and the devices as a non-access time with respect to each of the guest virtual machines accessing the devices via the device driver virtual machine; a storage unit that stores the operation profile information that matches the non-access time with the operation mode information representing the operation modes of the devices; a decision unit that decides the operation mode with reference to the operation profile information on the basis of the measured access time; and a transition control unit that transits the devices to the operation mode, so that this makes it possible to appropriately carry out power saving management of the devices not depending on a power saving function of the guest OS.