A control apparatus includes a learning portion which learns a control parameter by correcting a learning vector consisting of a plurality of variables and a control parameter based on a measurement vector. The control apparatus further includes an interpolation portion which computes the control parameter corresponding to current variables which represent a current environmental condition by interpolating the control parameter learned by the learning portion. The interpolation portion includes a selecting portion which selects three learning vectors from a plurality of learning vectors, and which computes the control parameter corresponding to the current variables by interpolating the control parameters on a flat surface including the selected three learning vectors.