An apparatus for detecting dispersion abnormality in air-fuel ratio between cylinders of a multiple-cylinder engine, including a waste gate passage which bypasses a turbine of a turbocharger, a waste gate valve which opens/closes the passage, an air-fuel ratio sensor installed in an exhaust passage on the downstream of an outlet of the passage, an abnormality detecting unit for detecting dispersion abnormality in air-fuel ratio between cylinders by comparing a parameter value correlating with a fluctuation of the sensor value with a predetermined threshold, and an exhaust speed increasing unit for increasing exhaust gas speed. The apparatus further includes a controller which controls the valve and the exhaust speed increasing unit, and the controller opens, when dispersion abnormality in the air-fuel ratio between cylinders is detected, the valve and increases exhaust speed by the exhaust speed increasing unit.