1. A portable computer which operates by an operating system (OS) corresponding to a predetermined language, the portable computer comprising: a keypad unit which includes a plurality of input keys each having at least one character labeled thereon and has a key array corresponding to a plurality of languages; a system unit to operate according to at least one input key value; and a control unit to determine the language according to which the OS operates, and to control the system unit to operate according to the input key value corresponding to an input key which is selected according to the key array corresponding to the determined language.