A film thickness predicting apparatus compares a measurement value of a copper plating formed on wiring grooves of various patterns measured using a TEG and a film thickness of the copper plating calculated based on a plating model and a condition file. The film thickness predicting apparatus then delivers optimal plating model from the comparison result and calculates the film thickness of the copper plating formed on a substrate surface to be designed using the optimal plating model. The film thickness predicting apparatus enables to conduct a highly accurate film thickness predicting simulation.