A technique for quantitatively expressing a manufacturing difficulty level of a photomask and for efficiently manufacturing the photomask is provided. A mask manufacturing difficulty level different for each mask layout, product, and mask layer is relatively recognized with a mask manufacturing load index calculated by a mask manufacturing load prediction system, and when layout correction is possible, the final layout is corrected to a layout with a low difficulty level, and a mask ordering party provides a mask manufacturer with information regarding the mask manufacturing difficulty level in an early stage. The mask manufacturing load index is expressed with a defect guarantee load index and a lithography load index.