An object of the invention is to provide an EGR cooler which enhances a cooling performance by increasing a ratio of the volume of a core portion which performs a heat exchange and enhances a pressure resistance strength. There is provided an EGR cooler having a core portion (1) in which a large number of flat tubes (4) through which exhaust gases pass are stacked one on another in an interior of a hollow cylindrical shell (7) to be joined to the shell (7) for heat exchange between the exhaust gases and a cooling fluid which flows around the tubes (4), a cylindrical inlet header (2) which is joined to an upstream side of the shell (7) in relation to a gas flow at one end thereof to thereby supply the exhaust gases into the core portion (1), and a cylindrical outlet header (3) which is joined to a downstream side of the core portion (1) in relation to the gas flow at one end thereof to thereby discharge the exhaust gases from the core portion (1), characterized in that the inlet header (2) and the outlet header (3) are joined to an outer surface of the shell (7), and the tubes (4)are joined to an inner surface of the shell (7) at those joint portions (13).
