PURPOSE: To simulate the etching operation of many layers by a method wherein an etching rate for other substances, to be etched, which have been exposed by deleting a point train is applied to the substances and a point train is moved by an etching rate which is peculiar to each substance.

CONSTITUTION: An oxide film 2 is formed on a silicon substrate 1; a nitride film 3 is formed on the oxide film 2. When a developed resist 4 exists on its upper part, a point train 5 is formed around each substance. An etching operation is made to progress clockwise; the intersection P of a point train is detected at each time step. At a stage where the intersection of the point train 5 has been detected, the point train is cut into pieces; a substance to be etched on the lower layer is exposed. Regarding a face (a flag is given as a candidate of a point to be moved to a point train included in the face) which comes into contact with an etching substance, an etching operation is continued at an etching rate which is decided by each substance to be etched and the etching substance.