Egr system abnormality diagnosis device

In an engine comprising a HPL-EGR mechanism (6) and the LPL-EGR mechanism (7) of MPL-EGR system, using a differential pressure sensor (89) detects LPL-EGR mechanism (7) having a low pressure EGR cooler ( 73) the upstream side pressure and the downstream pressure side pressure. When the LPL-EGR mechanism with respect to (7) in the reference pressure difference value clogged does not occur, the higher the detected actual pressure difference value, its deviation amount reaches a predetermined amount, it is determined in the low pressure EGR cooler (73) internal plugged. On the other hand, when the reference pressure difference value with respect to the detected actual pressure difference value is low, the amount of its deviation reaches a predetermined amount, it is determined that the pipe member outside the low pressure EGR cooler (73) (74, 75) internal plugged.