A virtual-machine control program includes an operational-status inquiry unit that inquires of another machine about a memory usage status of virtual machines realized on another machine; a swapping-target selecting unit that selects a virtual machine capable of being swapped for a virtual machine realized on a machine from among the virtual machines realized on another machine based on information obtained by the operational-status inquiry unit; and a swapping performing unit that swaps the virtual machine realized on the machine for the virtual machine selected by the swapping-target selecting unit. The virtual-machine control program enables to move the virtual machine to another machine without preparing a free space in advance.