Heat transfer members (H4, H3, H2, H1) are sequentially disposed within an exhaust port (18), within a pre-catalytic device (34), and on the downstream of a main catalytic device (35); the exhaust port (18), the pre-catalytic device (34), and the main catalytic device (35) being provided in an exhaust passage (33) of an internal combustion engine. The heat transfer surface density (heat transfer area/volume) of the heat transfer members (H4) on the upstream side of the exhaust passage (33) is the lowest, and that of the heat transfer members (H1) on the downstream side is the highest. Thus, even though the temperature of the exhaust gas is higher on the upstream side of the exhaust passage (33) than it is on the downstream side of the exhaust passage (33), a uniform heat transfer performance across all of the heat exchangers (H4, H3, H2, H1) may be maintained.