PURPOSE: To prevent the control calculation from being numerically unstable by setting the parameter of a model so as to set the weighing sum of the square sum of the deviation between an estimated value and the target value at a future time and the square sum of the changing part of a manipulated variable to be minimum based on the model of a process.

CONSTITUTION: When the parameter inputted to a parameter changing part 1 is confirmed, an estimating expression deciding part 2 decides the estimating expression of the model from the parameter. An estimating arithmetic part 3 executes arithmetic based on the estimating expression of the model decided by the estimating expression deciding part 2. The estimating arithmetic part 3 is composed of a conditional number arithmetic part 4 calculating the conditional number of τGG+λI which needs to obtain a retrograde train from the estimating expression, a judgement part 5 judging whether the conditional number is within an allowable range or not, and a correction part 6 correcting a weighing coefficient λ when it is not within the allowable range. When the conditional number is within the allowable range, the changed amount ΔU of the manipulated variable setting an evaluation function J to be minimum is obtained by using the present λ as it is, and outputted.