An apparatus for detecting imbalance abnormality in an air-fuel ratio between cylinders in a multi-cylinder internal combustion engine

An apparatus for detecting imbalance abnormality in an air-fuel ratio between cylinders in a multi-cylinder internal combustion engine, comprising: Fuel cut-off means for executing a fuel cut; Fat control means for performing a post-fuel cut rich control for enriching an air-fuel ratio immediately after the fuel cut; and Detecting means for increasing a fuel injection quantity for a predetermined target cylinder at least to detect an imbalance abnormality in an air-fuel ratio between cylinders based on a rotation variation of the target cylinder after increasing the fuel injection quantity, wherein the detection means performs the increasing of the injection amount in the middle of executing the post fuel cut rich control.