To reduce worsening of maneuvering stability due to side wind in an unsteady state wherein side wind is fluctuated.

Throughout a range of from the central part of a car body B to a rear end, fins 5 are arranged along the right and left sides 3 and the upper surface 4 of a car body B or the corner part of a rear surface. The sides 3 of the car body B and the outer surface of each fin 5 are smoothly interconnected. Even when side wind colliding with the side 3 of the car body B is fluctuated, side wind flows without peeling in the middle of a range of from the side 3 of the car body to the tip of the outer surface of the fin 5, and the flow is peeled at the tip of the outer side of the fin.