1. A parameter optimization method for real-time optimization of parameters related to control processing by a control system which controls a controlled object in an environment in which control conditions change dynamically, the method comprising: a first step of setting an acquisition range of operation information about operation of the controlled object when calculating an initial evaluated value, based on a statistical model created in the past and stored in a storage medium; a second step of acquiring the operation information in a current environment; a third step of calculating an evaluated value to evaluate results of the control processing based on the acquired operation information obtained in the second step; a fourth step of creating a statistical model using the calculated evaluated value as an explained variable, and the corresponding operation information as an explanatory variable; a fifth step of storing the created statistical model in the storage medium; a sixth step of calculating estimated values of parameters which provide an optimum solution to the statistical model stored in the storage medium in the fifth step; and a seventh step of updating the parameters used for the control processing based on the calculated estimated values of the parameters; wherein the parameters are optimized in real time through repetition of the second to seventh steps at predetermined time intervals after execution of the first step.