An object of the present invention is to provide a technology that enables to detect a fault of a PM trapper with improved accuracy. According to the present invention, a plurality of temperature sensors 10 are provided in an exhaust passage 9 just downstream of a PM trapper 17 in such a way that their temperature detection elements are positioned on a plane that is perpendicular to an imaginary center axis of the exhaust passage 9. A change in the radial direction temperature distribution of the exhaust gas flowing out of the PM trapper 17 upon occurrence of a fault in the PM trapper 17 is detected from measurement values of the temperature sensors 10, and a fault of the PM trapper 17 is detected based on this radial direction temperature distribution. Since the measurement values of the temperature sensors 10 are unlikely to be affected by the amount of PM deposited on the PM trapper 17, detection of a fault of the PM trapper 17 can be achieved with improved accuracy.