1. A plant control system for controlling a plant, comprising: an operation signal generation part which calculates a control operational signal for the plant to be controlled, by using a measurement signal which has measured an operation state of the plant; a measurement signal database which stores measurement signals of the plant; an operation signal database which stores control operational signals generated by the operation signal generation part, for the plant; a numerical calculation execution part which analyzes an operation characteristic of the plant, to calculate a numerical calculation result for use in simulation modeling of the plant; a numerical calculation database which stores numerical calculation results from the numerical calculation execution part; a simulation model part preparing a simulation model which simulates a control characteristic of a plant when a subject control operational signal is supplied to the plant, according to information on the numerical calculation result from the numerical calculation database; a learning part which learns a plant operation method by using the simulation model, to generate learning information data; a learning information database which stores learning information data from the learning part; a control logic database which contains control logic data used by the operation signal generation part, in the calculating of the control operational signal; a pattern generation part which generates pattern data expressing a state input, based on subject learning information data; a pattern database which stores the pattern data generated in the pattern generation part; and a learning result determination part which selects a learning result having a preferable control effect from plural learning results obtained by using a plurality of patterns; wherein the control operational signal is calculated by the operation signal generation part according to the learning result selected by the learning result determination part.