PURPOSE: To input characters efficiently by allowing a character processor which converts a character string into another optional character string to reuse readings which are inputted before.

CONSTITUTION: The readings of characters inputted on a keyboard KB are transferred to and stored in a key buffer KBF by an input processing part IP if the character string is inputted after a conversion key HK is operated. The data in the key buffer KBF is supplied to a conversion processing part TP and a conversion table TBL is referred to convert the reading inputs into a corresponding character string, which is stored in a display buffer DBF and displayed.