PURPOSE:To detect all short areas in a short time by dividing 1st and 2nd wiring patterns into basic divided patterns and checking whether the data proper to each wiring is shared or not and whether those wirings are connected to each other or not. CONSTITUTION:A process executing means 2 divides 1st and 2nd wiring patterns into the basic divided patterns of a power supply wiring 5 and a ground wiring 11 and stores these patterns into an auxiliary storage means 3 based on the power supply pattern of the 1st wiring pattern and the ground pattern of the 2nd wiring pattern which are supplied from a data input means 1. Then the means 2 recognizes the inclusion relationships among the power supply label data 10 proper to a power supply, the ground label data 16 proper to the ground, and those divided patterns and furthermore the connecting relation between both wirings 5 and 11 based on the contents of the means 3. Then a point where both data 10 and 16 are shared and both wirings 5 and 11 are connected to each other is decided as a short area and delivered via a plotting means 4. In such an automatic detection mechanism, all short areas can be recognized and detected in a short time.