PURPOSE: To select and change the language of characters displayed on the display means of a numerical controller.

CONSTITUTION: For information whose display character string needs to be changed corresponding to an in-use language in information to be displayed, this numerical controller has a display unprocessed data data generating means 1 which generates display unprocessed data changed into the address corresponding to the information, an in-use language selecting means 2 which selects and holds one language out of plural languages, and a display character string data file 3 which contains a matrix of character strings written in plural languages by pieces of information to be changed corresponding to the in-use language and generates the character string corresponding to a received address signal and the in-use language. Further, the controller has a display means 4 which receives the display unprocessed data generated by the display unprocessed data generating means 1, sends the address in the display unprocessed data as the address signal to the display character string data file 3, and substituting the address in the display unprocessed data in the character string to be sent back and written in the in-use language to display it.