In an exhaust gas purifying apparatus for a diesel engine having a diesel particulate filter provided in an exhaust pipe, a pressure loss at the filter is detected. An accumulated amount of diesel particulates in the filter is calculated based on the pressure loss and a map for a relationship between the pressure loss and the accumulated amount. A compulsory re-generating operation is carried out when the calculated accumulated amount reaches at a predetermined threshold value, which is decreased to a smaller value depending on a combustion amount of the diesel particulates which are combusted and removed from the filter as a natural re-generating operation.