PROBLEM TO BE SOLVED : To provide an interior coordinate system which enables to perform interior designs superior in effectiveness, and providing at a low cost and good habitability. SOLUTION : The interior coordinate system 10 of this invention is provided with following parts and data bases(DB); a network processing part 11, a web DB 12, a room layout DB 13, an interior elements information DB 16, an interior elements information gathering part 14, an interior elements information classification part 15, a customer interior information extracting part 17, a customer interior information DB 18, an interior design part 19 which draws up presentation sheets based on the room layout information, the interior elements information and the customer interior information, an output part 21 such as a printer, etc., and an order processing part 22.