The present invention provides a control apparatus for a plant, which can suppress excessive correction for a spiky disturbance being applied and maintain a good controllability, when controlling the plant, which is a controlled object, with the self-tuning regulator. A detected equivalent ratio KACT is input to a high-pass filter 33, and a high-pass filter output KACTHP is input to a parameter adjusting mechanism 42. The parameter adjusting mechanism 42 calculates a corrected updating vector (KID·dθ(k)) by multiplying an updating component dθ of a model parameter vector by a correction coefficient KID, and adds the corrected updating vector to a preceding value θ(k−1) of the model parameter vector, to thereby calculate a present value θ(k). The correction coefficient KID is changed from “1.0” to a value near “0” upon detection of the spiky response where an absolute value of the high-pass filter output KACTHP increases.