This control apparatus obtains a relation (trade-off line) between NOx generation amount and PM generation amount with EGR ratio serving as a parameter from an NOx generation amount estimation model which calculates the NOx generation amount on the basis of the oxygen mole concentration of intake gas and a PM generation amount estimation model which calculates the PM generation amount on the basis of an excess air factor. Further, the control apparatus obtains a straight line (ratio determination line) which passes through a point (appropriate point A) corresponding to a combination of steady-condition appropriate values of the NOx generation amount and the PM generation amount under the present operating conditions and which has a slope K determined in consideration of a regulation value based on a law relating to emission control. The control apparatus uses an intersection (target point B) between the trade-off line and the ratio determination line as an emission target value, and sets an EGR ratio target value Regrt to an EGR ratio corresponding to the target point B.