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 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 automatically identify the predetermined language of the currently operating OS, and to control the system unit to operate according to the input key value corresponding to an input key that has been selected from among a first plurality of input keys according to the key array corresponding to the identified predetermined language of the currently operating OS, wherein at least one first input key among the first plurality of input keys is assigned a non-alphanumeric function for a first determined language, and the non-alphanumeric function of the first input key is changed to a character in response to changing the predetermined language to a second language.