Abstract: Each of a plurality of, as many as three or more, processes is executed by one of a first virtual machine and a second virtual machine, and each of the first and second virtual machines executes at least one of the processes. At the execution of each of the processes, a virtual memory unit corresponding to the process is referred to. Based on ranks each assigned in advance to one of the processes, a processor changes an assignment destination of a physical memory area currently assigned to each of virtual memory units, except for a virtual memory unit corresponding to a last-rank process, to a virtual memory unit corresponding to a next-rank process following a process corresponding to a virtual memory unit to which the physical memory area is currently assigned.