A first defect distribution superimposed image is formed by superimposing defect distributions on individual substrates processed by a causal equipment unit candidate on one another. Second defect distribution superimposed images are formed by superimposing, on one another, defect distributions on individual substrates processed by equipment units other than the causal equipment unit candidate in one same step as that executed by the causal equipment unit candidate. The first defect distribution superimposed image and the second defect distribution superimposed images are displayed in contrast on one display screen.