An exhaust gas purifying apparatus for a diesel engine has a filter provided in an exhaust pipe of the engine for trapping diesel particulates contained in exhaust gas. The filter is re-generated when an accumulated amount of the diesel particulates exceeds a predetermined value. An electronic control unit estimates the accumulated amount of the diesel particulates from a pressure loss at the filter, based on an accumulation characteristic in which the pressure loss is related to the accumulated amount of the diesel particulates, and corrects the accumulation characteristic depending on flow velocity of the exhaust gas.