Cpu virtualization method

A method for virtualizing a CPU is provided to stably and efficiently perform para-virtualization of an OS(Operating System), which is operated in a CPU having two CPU modes, in one CPU mode, and keep stability of a kernel and shorten a development time by minimizing modification of the kernel of a current OS. A virtualizer operates a plurality of guest OSs at the same time and executed in a privilege mode of a processor is provided. A non-privilege mode of the processor is divided into at least two virtual lower modes, which are hierarchically graded(S106,S108). A privilege command is transited to the virtualizer when the privilege command is generated in the virtual lower modes. The virtualizer transfers the privilege command to a hierarchical mode processing the privilege command among the virtual lower modes(S114), and the hierarchical mode processing the privilege command processes the privilege command, and the mode is kept or transited to the other virtual lower mode(S116).