EXHAUST EMISSION CONTROL DEVICE OF INTERNAL COMBUSTION ENGINE

The present invention is provided with an NOx catalyst 17 provided in the exhaust passage of an internal combustion engine capable of lean burn and adapted to release and reduce absorbed NOx by a reducing agent, a reducing agent supplying means 19 provided in the exhaust passage on the upstream side of the NOx catalyst 17, a load detecting means for detecting the load of an internal combustion engine 1, and a reducing agent addition control means for controlling the reducing agent addition period and the reducing agent addition interval on the basis of the load of the internal combustion engine 1. The addition period and the addition interval for the reducing agent are controlled taking into account, for example, the degree to which reducing agent adheres to the wall surface in the exhaust passage depending on the velocity, temperature, etc., of the exhaust of the internal combustion engine 1, whereby a sufficient amount of reducing agent is supplied to the NOx catalyst side independently of the operating condition. Thus, even if the operating condition of the internal combustion engine is changed, it is always possible to supply an appropriate amount of reducing agent to the NOx catalyst.