PURPOSE: To improve processing efficiency and to enable data conversion with high reliability concerning the data converting method to convert a design data prepared by a computer support designing device to a manufacture data.

CONSTITUTION: A layout data prepared by using a pattern preparing device 1 is stored in a database 21, and data conversion information prepared by using a conversion information preparing device 22 is stored in the database 21. Then, the layout data added the data conversion information is outputted to a magnetic tape 23 as one file. This magnetic tape 23 is loaded to a data converter 8, and the layout data is converted to the manufacture data and outputted to a magnetic tape 9.