To provide an exhaust emission control device accurately sensing decrease in the real value of the fuel injection amount from a fuel adding valve from the command value owing to deterioration of the fuel adding valve and of calculating the correction value for proper injection amount.

From the fuel adding valve, the fuel is injected into an exhaust valve with a prescribed injection amount Qadd and a prescribed cyclic period Tadd of injection within the prescribed period of time during the period in which a NOx catalyst does not conduct NOx reduction nor SOx reduction. The A/F value is measured by A/F sensors installed upstream of the NOx catalyst and downstream (A/F measured value), and therefrom the mean is calculated (A/F mean value). The change rate pertaining to the time of the A/F mean value is calculated, and the mean with the change rate exceeding the prescribed value is excluded. From the obtained A/F mean value, the actual injection amount from the fuel adding valve is calculated, and the difference between the command value of the injection amount and the actual injection amount is used as the correction value for the injection amount.