A control apparatus that is capable of maintaining both the control resolution and the control accuracy at respective high levels even when at least one of the nonlinearity and the frequency characteristic of a controlled object varies. A control apparatus 1 that control a cam phase Cain by a phase control input Ucain includes two controllers 102 and 103. The two-degree-of-freedom response-specifying controller 102 calculates a follow-up control input Rsld as a value for causing the cam phase to follow a target cam phase Cain_camd. The DSM controller 103 calculates a phase control input Ucain by modulating the follow-up control input Rsld, and in the calculation, the repetition period at which the phase control input Ucain is calculated is selected from two repetition periods .DELTA.T1 and .DELTA.T2 according to engine speed NE, a cam phase Cain, and a valve lift Liftin.