To shorten an LSI development term by effectively inspecting and modifying data for exposure which is not corrected yet or corrected already.

In response to a menu item (depressed command button) selected at a step S12, the operation of a pattern for exposing a wafer is advanced to a step S13 and a step 14. Then, it is displayed at a step S15 and inspected at a step S16 or modified at a step S17. Besides, the operation of a block pattern on a stencil mask is advanced to the step S13 and a step S24. Then, it is displayed at a step S25 and inspected at a step S26 or modified at a step S27. Besides, the exposure simulation of the pattern for exposing a wafer is executed at the step 16 and the result thereof is displayed at the step S15. Then, pattern data for exposing wafer is modified based on the result of the exposure simulation at the step S17. When the block pattern on the stencil mask is modified, the block pattern developed in the pattern data for exposing wafer is also modified in a lump.