An exhaust emission control device includes a first detection unit for detecting a NOx adsorption amount and an oxygen storage amount of a three-way catalyst and a NOx purification catalyst during rich spike, a second detection unit for detecting the oxygen storage amount of the three-way catalyst and the NOx purification catalyst until the output of a second air-fuel sensor becomes lean after the rich spike, and a deterioration determination unit for determining deterioration of the NOx purification catalyst based on a detected value of the first detection unit and that of the second detection unit.