1. A computer readable, non-transitory storage medium storing a virtualization program to run a host virtual machine manager and a guest virtual machine manager by being executed in a physical computer including a physical processor and a memory, the virtualization program stored on the computer readable, non-transitory storage medium causing the physical processor to execute the steps of: storing, by the guest virtual machine manager, first control information for specifying a status of a virtual processor to execute a user program to the memory; storing, by the guest virtual machine manager, second control information for specifying a status of the virtual processor to execute the guest virtual machine manager to the memory; managing, by the host virtual machine manager, an operation mode flag which indicates which of the user program and the guest virtual machine manager is operating on the virtual processor; updating, by the host virtual machine manager, third control information for specifying a status of the physical processor with one of the first control information and the second control information in accordance with a determination of which of the user program and the guest virtual machine manager is to be executed by referring the operation mode flag; and issuing, by the host virtual machine manager, a first control instruction for the physical processor to execute one of the user program and the guest virtual machine manager based on the third control information.