Abstract: When model statements in an origin language, model statements in a target language, and conversion rules for word (variable) sections are inputted from the screen of a conversion rule input means, a conversion rule generation means generates a conversion rule according to this input and stores it in the conversion rule database. The conversion rule is composed of a search key, a word conversion direction section, and a target language generation program. The search key is used when a conversion rule needed for the conversion of an unconverted origin program is searched for in a database and fetched, the word conversion direction section is used for calling the word conversion table or the word conversion program, and the target language generation program is used for generating a converted target program. The conversion rule input means, conversion rule generation means, and conversion rule drive means do not depend on the origin language and target language of the languages involved in conversion.