To provide a control method for an exhaust emission control device having high durability at a low cost by estimating an exhaust temperature on the basis of an engine speed and a rack position without using a temperature sensor for measuring the exhaust temperature when controlling an engine and the exhaust emission control device.

When controlling the engine, instead of detecting the exhaust temperature Tg with the temperature sensor, a temperature index TP related to the exhaust temperature Tg is computed on the basis of the engine speed Ne and the rack position R of a fuel control rod for fuel injection of the engine. When the temperature index TP exceeds a predetermined determination value TPc, a determination that the exhaust temperature Tg exceeds the predetermined exhaust temperature Tgc is done.