1. A method for register mapping in a virtual system that implements a hypervisor and at least two operating systems that are operable while executing at least two hardware threads, the method comprising: preparing a register pool that includes a plurality of registers for mapping; preparing a mapping table that has a register identifier (ID) and information related to each of a plurality of parameters that express an operational state of the virtual system for each of the registers; acquiring, at the time a register access request is issued by a hardware thread, the register ID for an access target and information related to each of the plurality of parameters that express the operational state during operation; and setting one of the registers, for which the acquired register ID and information related to each of the plurality of parameters match the register ID and information for each of the plurality of parameters within the mapping table, as a mapped register to be accessed per the register access request.