A gas pipe for sending exhaust gas discharged from an engine to an air-intake system of the engine, the gas pipe comprising: first fins, wherein the first fins project downward in a vertical direction; and second fins, wherein the second fins project upward in the vertical direction, the first fins and the second fins being configured such that: a) the first fins project from a first region of an inner peripheral surface of the gas pipe; b) the second fins project from a second region of the inner peripheral surface of the gas pipe, the second region being opposed to the first region; c) the second fins face the first fins across a predetermined space; d) the first fins are provided along an exhaust-gas flow direction; e) the second fins are provided along the exhaust-gas flow direction; f) the first fins are provided to be adjacent to each other across a predetermined space in a direction perpendicular to the exhaust-gas flow direction; g) the second fins are provided to be adjacent to each other across a predetermined space in the direction perpendicular to the exhaust-gas flow direction; h) a thickness of the first fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the first fins, such that both surfaces of each of the first fins along the exhaust-gas flow direction are inclined; and i) a thickness of the second fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the second fins, such that both surfaces of each of the second fins along the exhaust-gas flow direction are inclined; characterized in that: j) a tilt angle of either ones of inclined surfaces of the first fins and inclined surfaces of the second fins is larger than the tilt angle of the other ones of the inclined surfaces of the first fins and the inclined surfaces of the second fins; k) the second fins have a height that is smaller than the height of the corresponding first fins. first fins, wherein the first fins project downward in a vertical direction; and second fins, wherein the second fins project upward in the vertical direction, the first fins and the second fins being configured such that: a) the first fins project from a first region of an inner peripheral surface of the gas pipe; b) the second fins project from a second region of the inner peripheral surface of the gas pipe, the second region being opposed to the first region; c) the second fins face the first fins across a predetermined space; d) the first fins are provided along an exhaust-gas flow direction; e) the second fins are provided along the exhaust-gas flow direction; f) the first fins are provided to be adjacent to each other across a predetermined space in a direction perpendicular to the exhaust-gas flow direction; g) the second fins are provided to be adjacent to each other across a predetermined space in the direction perpendicular to the exhaust-gas flow direction; h) a thickness of the first fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the first fins, such that both surfaces of each of the first fins along the exhaust-gas flow direction are inclined; and i) a thickness of the second fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the second fins, such that both surfaces of each of the second fins along the exhaust-gas flow direction are inclined; characterized in that: j) a tilt angle of either ones of inclined surfaces of the first fins and inclined surfaces of the second fins is larger than the tilt angle of the other ones of the inclined surfaces of the first fins and the inclined surfaces of the second fins; k) the second fins have a height that is smaller than the height of the corresponding first fins. a) the first fins project from a first region of an inner peripheral surface of the gas pipe; b) the second fins project from a second region of the inner peripheral surface of the gas pipe, the second region being opposed to the first region; c) the second fins face the first fins across a predetermined space; d) the first fins are provided along an exhaust-gas flow direction; e) the second fins are provided along the exhaust-gas flow direction; f) the first fins are provided to be adjacent to each other across a predetermined space in a direction perpendicular to the exhaust-gas flow direction; g) the second fins are provided to be adjacent to each other across a predetermined space in the direction perpendicular to the exhaust-gas flow direction; h) a thickness of the first fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the first fins, such that both surfaces of each of the first fins along the exhaust-gas flow direction are inclined; and i) a thickness of the second fins in the direction perpendicular to the exhaust-gas flow direction is gradually thinned toward a projection direction of the second fins, such that both surfaces of each of the second fins along the exhaust-gas flow direction are inclined; characterized in that: j) a tilt angle of either ones of inclined surfaces of the first fins and inclined surfaces of the second fins is larger than the tilt angle of the other ones of the inclined surfaces of the first fins and the inclined surfaces of the second fins; k) the second fins have a height that is smaller than the height of the corresponding first fins.