In the engine including an MPL-EGR system having an HPL-EGR mechanism 6 and an LPL-EGR mechanism 7, a pressure difference between upstream side pressure and downstream side pressure of a low pressure EGR cooler 73 provided in the LPL-EGR mechanism 7 is detected by a pressure difference sensor 89. When an actual pressure difference value detected is higher than a reference pressure difference value in a state where no blocking occurs in the LPL-EGR mechanism 7, and the deviation amount therebetween reaches a predetermined amount, it is determined that the blocking occurs in the inside of the low pressure EGR cooler 73. In contrast, when the actual pressure difference value detected is lower than the reference pressure difference value, and the deviation amount therebetween reaches a predetermined amount, it is determined that the blocking occurs in the inside of the pipe members 74 and 75 except the low pressure EGR cooler 73.