An exhaust gas purifying apparatus for an internal combustion engine, including a filter provided in an exhaust system of the engine for trapping particulates in exhaust gases, and a pressure difference sensor for detecting a pressure difference between an upstream side pressure of the filter and a downstream side pressure of the filter. A non-frozen state of the pressure difference sensor is determined based on at least one of a first parameter relevant to an exhaust gas temperature of the engine and a second parameter relevant to an atmospheric temperature. An abnormality of the filter is determined based on a result of the non-frozen state determination.