To provide an apparatus for detecting a fluctuation abnormality of air-fuel ratios among cylinders of a multi-cylinder internal combustion engine, which increases a detecting opportunity.

The apparatus includes: a changing means for changing an operation angle of an intake valve according to an operating condition of the internal combustion engine; a fuel cutting means for executing a fuel cut when a predetermined condition is established; a rich control means for controlling an air-fuel ratio to be richer than a predetermined standard value; and a detecting means for detecting the fluctuation abnormality of the air-fuel ratio among the cylinders, when the operation angle S is not more than a predetermined value Sx, and when the rich control is being made by the rich control means just after return from the fuel cut.