1. An estimating polynomial generating device comprising: an analysis data storer storing in advance analysis data comprising input parameter data and corresponding output parameter data; a function surface storer storing in advance an equation for a function surface for limiting a relationship between the input parameter and the corresponding output parameter after a homothetic conversion; a homothetic conversion equation storer storing in advance a homothetic conversion equation for performing homothetic conversion of the input parameter and the corresponding output parameter; a homothetic conversion parameter searcher searching and establishing factors of the homothetic conversion equation using the analysis data, the equation for the function surface, and the homothetic conversion equation; and an estimating polynomial calculator calculating an estimating polynomial for estimating an output parameter value from an input parameter value by combining the function surface equation and the homothetic conversion equation for which the factors have been established, wherein the homothetic conversion parameter searcher uses a searching equation wherein the homothetic conversion equations are substituted into the equation for the function surface to search for the factors in the homothetic conversion equations that minimize a sum of errors each obtained for each of the analysis data by calculating, for each of the analysis data, the error in the output parameter calculated by substituting the analysis data into the searching equation.