To speed up memory reconfiguration processing in a virtual machine system.

Two types of rights, management and usage rights, are provided as rights to memory areas and managed in a real memory management part 1110. When a memory area X for a first virtual machine is reallocated to a second virtual machine, a real memory configuration control part 1120 assigns only the management right first, and assigns the usage right when the second virtual machine actually accesses the memory area X. The assignment of the usage right will require paging out/swapping and take time if the first virtual machine has written data in the memory area X, but the assignment of only the management right does not require such processing. The management right can thus be assigned quickly. The second virtual machine having the management right can acquire the usage right anytime to access the memory area X, and thus substantially has the memory area allocated.