A virtual machine control method and a virtual machine system are disclosed. In the case where a guest program can be operated in a plurality of address translation modes and the same guest virtual address is translated into different host real addresses in each address translation mode, the illegal access to a host real address by illegal address translation by double registration in the same page table is avoided, and the address translation mechanism is efficiently operated. A plurality of host page tables are prepared in the main storage, and one of the host page tables is selected with the change in address translation mode of the guest program. The bottom address of the selected host page table is set in the host page table register thereby to switch the host page table.