PURPOSE: To efficiently execute the processing by providing a means for replacing an input sentence with a different expression executed by first natural language, based on a result of analysis, converting the input sentence whose literal translation is difficult to a sentence of an equivalent expression whose literal translation can be executed, and thereafter, converting it to natural language.

CONSTITUTION: A Japanese sentence inputted from an input device is subjected to word division and syntax analysis by an analyzing device 2, and with respect to this result, by a rewriting device 3, the above word and syntax information are replaced, based on a rewriting table 8. Subsequently, in a converter 4, the word and the syntax information are converted from Japanese to English by using a conversion dictionary 9, and in a generating device 5, an English sentence is generated by using a generation dictionary 10, and thereafter, it is outputted from an output device 6. In such a way, a sentence of original language whose literal translation is difficult is formed so that the mechanical processing can be executed, and the preliminary processing is executed, therefore, a sentence of original language whose literal translation is difficult can also be processed efficiently.