1. A model generating method of generating a model to estimate a state of an object under a predetermined control condition, comprising the steps of: calculating error data indicative of a difference between actual measurement data obtained by measuring a state of said object corresponding to input data and simulation data obtained by inputting said input data to a physical model in which physical properties of said object are considered; deriving a correction function for correcting said simulation data so as to be close to said actual measurement data based on a change in said error data corresponding to said input data; and generating a final model of said object by combining said physical model and said correction function.