To provide an adapter for cooling exhaust of an internal combustion engine, inhibiting concentration of a heat receiving amount on an exhaust manifold side.

The inner surface 40 of an exhaust flow passage 32 has an annular swell part 40c swelling inward in the radial direction and is formed with two tapered parts 40a, 40b on both sides. A large amount of heat is received from the exhaust at the tapered part 40a on an exhaust port 18 side, and a heat receiving amount from the exhaust is small at the tapered part 40b on an exhaust manifold 22 side. Further, the opening diameter of an exhaust discharge port 28 is larger than the opening diameter of an exhaust manifold 22 so that a connection area of both sides is reduced sufficiently and a heat receiving amount from the exhaust manifold 22 can be suppressed sufficiently. Accordingly, on the exhaust manifold 22 side of the adapter 20 for cooling the exhaust, even when heat is transmitted from the exhaust manifold 22, a total heat receiving amount can be reduced and the concentration of the heat receiving amount can be inhibited.