To specify which of two systems of variable intake valve lift devices 17 and 18 installed in two cylinder groups is abnormal.

An ECU 23 diagnoses the presence or absence of an abnormality in the variable intake valve lift devices 17 and 18 according to whether the ratio of the varied amount of the air-fuel ratio of each cylinder calculated to the varied amounts of the air-fuel ratios of all cylinders calculated is smaller than an abnormality determination value or not when the abnormality of the variable intake valve lift devices 17 and 18 of two cylinder groups is diagnosed. Also, a specific cylinder among all cylinders in which the air-fuel ratio becomes maximum (leanest) and a specific cylinder in which the air-fuel ratio becomes minimum (richest) are obtained. By the relation between a control mode for the variable intake valve lift devices 17 and 18 of each cylinder group, the cylinder group to which the cylinder with the maximum air-fuel ratio belongs, and the cylinder group to which the cylinder with the minimum air-fuel ratio belongs, it is specified which of the variable intake valve lift device in the cylinder groups is abnormal.