1. A control system for a plant, comprising: identifying means for identifying a model parameter vector of a controlled object model which is obtained by modeling said plant, based on an input and an output of said plant; and a sliding mode controller for controlling said plant using the model parameter vector identified by said identifying means; said identifying means comprising: identifying error calculating means for calculating an identifying error of the model parameter vector; updating vector calculating means for calculating an updating vector according to said identifying error; and updating vector correcting means for correcting said updating vector by multiplying a past value of at least one element of said updating vector by a predetermined value which is greater than 0 and less than 1; wherein said identifying means calculates the model parameter vector by adding the corrected updating vector to a reference vector of the model parameter vector.