1. A virtualization method for a machine having a processor and memory connected to the processor, the machine includes: a first virtual machine manager that is executed by the processor and manages a plurality of virtual machines generated by virtually dividing a physical resource of the machine, and a second virtual machine manager that is executed on each of the virtual machines and respectively manages an operating system to respectively execute an application, wherein the memory includes: first management information and second management information, the first management information is stored in the memory by the first virtual machine manager and manages a status of the first virtual machine manager and the second virtual machine manager, and the second management information is stored in the memory by the second virtual machine manager and manages a status of the second virtual machine manager and one of the respective operating system and the respective application, and wherein the processor includes: a register to store control information for controlling the processor, and a shadowing function to read a particular address of the memory, indicated by the first management information in accordance with a read operation on the register when first shadowing information, included in the first management information, indicates active status, the virtualization method comprising: detecting, by the first virtual machine manager, a call from the second virtual machine manager based on an activation of one of the operating system or the application managed by the second virtual machine manager; determining, by the first virtual machine manager, whether second shadowing information, which is included in the second management information, indicates active status or not; changing, by the first virtual machine manager, the first shadowing information to indicate active status when it is determined that the second shadowing information indicates active status; converting, by the first virtual machine manager, a second address, which is included in the second management information and uniquely identifies a location of address space of the memory allocated to the virtual machine corresponding to the second virtual machine manager, to a first address which uniquely identifies an address location in the memory; storing, by the first virtual machine manager, the first address to the first management information in the memory; activating, by the first virtual machine manager, the one of the operating system or the application managed by the second virtual machine manager; sending, by the processor, a specified value, read from the first address of the memory based on the first management information, to the one of the operating system or the application managed by the second virtual machine manager in accordance with a read operation on the register from the one of the operating system or the application managed by the second virtual machine manager; detecting a write request issued to the register from one of the operating system and the application; and using the shadowing function and writing the specified value to the first address, wherein the specified value corresponds to a value to be written in accordance with a write request issued to the register from one of the operating system and the application.