The entire surface of a photomask 101 is inspected after data and parameters of the lithography simulator are set in the operation setting screen of a control computer 110 and after the inspection system 100 is calibrated. The coordinates of a portion or portions determined in the inspection to be a defect are written into an XML file. When the inspection system 100 is in the die-to-database inspection mode, the control computer 110 reads pattern data from the database, which data is used by the inspection system 100 to generate reference data, and then converts the read pattern data into OASIS format, which is highly versatile. The optical image captured by the inspection system 100 is converted into a bitmap. These data are sent to the lithography simulator, together with simulation operating conditions and the image data that was used to calibrate the inspection system 100.