An exhaust gas purifying apparatus for an internal combustion engine having a particulate filter provided in an exhaust system of the engine. Regeneration control is performed of burning particulates accumulated in the particulate filter. An oxygen concentration in exhaust gases flowing into the particulate filter is detected, and a flow rate of oxygen flowing into the particulate filter is calculated according to the detected oxygen concentration. An inflowing oxygen amount is calculated by integrating the oxygen flow rate when performing regeneration control. It is determined that an abnormality has occurred if the inflowing oxygen amount at a time when regeneration control ends is equal to or less than a predetermined amount.