To perform format conversion with high quality and to facilitate operation in a conversion environment.

A sender side generates an intermediate file through a sender- side drawing data part 11 which sends and receives drawing data between different CAD systems. This intermediate file is sent to a drawing information extracting process part 12 and common information and drawing data information of a CAD drawing are extracted. The common information and drawing data information are supplied to a conversion condition check part 13 and the contents of a conversion format are checked. This check part 13 defines conversion environment and specifies a conversion format for the check according to a conversion information library 14. When conversion conditions are changed, the extracted common information and drawing data information are converted into specified drawing data information according to the format specified by the conversion information library 14. The contents of the format converted by the conversion condition check part 13 are supplied to a receiver- side drawing data part 18 through a conversion part 17.