Exhaust gas purifying method and apparatus for internal combustion engine

An exhaust gas purifying method for an internal combustion engine (1), including determining an amount of particulates in an exhaust gas which is accumulated in a particulate filter (4) disposed within an exhaust passage (10) of the engine (1), determining whether the particulate filter (4) is at an adequate state for regeneration, and executing regeneration of the particulate filter (4) by controlling oxygen concentration in the exhaust gas depending on the amount of the trapped particulates when it is determined that the particulate filter is at the adequate state and the amount of the accumulated particulates exceeds a first preset value. An exhaust gas purifying apparatus including a plurality of sensors (21,22,23,24,25) detecting parameters relative to an engine operating condition, a particulate filter (4) operative to accumulate particulates present in exhaust gas flowing thereinto and a controller (20) programmed to implement the determinations and the execution of regeneration of the method.