An exhaust gas heat exchanger having stacked flat tubes comprising: a stacked tube body configured by stacking a plurality of flat tubes in multiple tiers with spaces therebetween and arranged inside a case; the exchanger configured such that: exhaust gas flows in from one end part of the stacked tube body in a tube axis direction, circulates through an inside of each flat tube, and flows out from the other end part of the stacked tube body in the tube axis direction; and cooling water introduced from cooling water introduction parts provided for the case is supplied to the one end part to circulate along an exterior surface side of each flat tube, wherein: the cooling water introduction parts (5, 6) are provided in two locations for the case and introduction directions of the cooling water from each of the cooling water introduction parts (5, 6) into the inside of the case are set in mutually opposite directions; each of the introduction directions is parallel to a flat surface of the flat tube in the stacked tube body and perpendicular to the axis direction of the flat tube; each of the two cooling water introduction parts (5, 6) is provided with a baffle plate having cutout parts; the exchanger is configured such that the introduced cooling water passes through these cutout parts and is distributed to the one end part of the stacked tube body in the tube axis direction; characterised in that the two baffle plates are configured such that respective distribution main portions of the cooling water flow toward spaces between mutually different layers of the stacked tube body, so that each cooling water that flows out from the cutout parts of the two baffle plates so as to face mutually do not interfere mutually at a centre part of one end part of the stacked tube body in the tube axis direction. exhaust gas flows in from one end part of the stacked tube body in a tube axis direction, circulates through an inside of each flat tube, and flows out from the other end part of the stacked tube body in the tube axis direction; and cooling water introduced from cooling water introduction parts provided for the case is supplied to the one end part to circulate along an exterior surface side of each flat tube, wherein: the cooling water introduction parts (5, 6) are provided in two locations for the case and introduction directions of the cooling water from each of the cooling water introduction parts (5, 6) into the inside of the case are set in mutually opposite directions; each of the introduction directions is parallel to a flat surface of the flat tube in the stacked tube body and perpendicular to the axis direction of the flat tube; each of the two cooling water introduction parts (5, 6) is provided with a baffle plate having cutout parts; the exchanger is configured such that the introduced cooling water passes through these cutout parts and is distributed to the one end part of the stacked tube body in the tube axis direction; characterised in that the two baffle plates are configured such that respective distribution main portions of the cooling water flow toward spaces between mutually different layers of the stacked tube body, so that each cooling water that flows out from the cutout parts of the two baffle plates so as to face mutually do not interfere mutually at a centre part of one end part of the stacked tube body in the tube axis direction. the cooling water introduction parts (5, 6) are provided in two locations for the case and introduction directions of the cooling water from each of the cooling water introduction parts (5, 6) into the inside of the case are set in mutually opposite directions; each of the introduction directions is parallel to a flat surface of the flat tube in the stacked tube body and perpendicular to the axis direction of the flat tube; each of the two cooling water introduction parts (5, 6) is provided with a baffle plate having cutout parts; the exchanger is configured such that the introduced cooling water passes through these cutout parts and is distributed to the one end part of the stacked tube body in the tube axis direction; characterised in that the two baffle plates are configured such that respective distribution main portions of the cooling water flow toward spaces between mutually different layers of the stacked tube body, so that each cooling water that flows out from the cutout parts of the two baffle plates so as to face mutually do not interfere mutually at a centre part of one end part of the stacked tube body in the tube axis direction.