An EGR cooler includes a heat exchanging core which has a plurality of tubes, an upstream-side gas tank portion upstream of the tubes and a downstream-side gas tank portion downstream of the tubes. A water tank portion forms a first water passage around the tubes and forms a second water passage around the upstream-side gas tank portion. A double pipe portion forms a gas passage which communicates with the upstream-side gas tank portion and forms an annular water passage which communicates with the second water passage. A water inflow pipe is connected to the double pipe portion such that the cooling water flows into the annular water passage, and a water outflow pipe that is connected to the water tank portion such that the cooling water flows out from the first water passage.