To maintain a constant section modulus without molding the axial part of a pipe member in a flat shape, while the pipe member is kept in a round pipe and stably attach and fix all components including other member to the axial side face of the pipe member.

This attaching structure is provided with a fixing member 3 comprising a head part 3a having a curved surface 30 maching with the axial side surface of a pipe member 1 and a flat surface 31 for bearing other member 2 on its plane and a cylindrical leg part 3b raised and formed integrally from the curved surface 30 of the head part 3a. The leg pasry 3b of the member 3 is fitted into an opening part 4 provided on the axial side surface of the pipe member 1 and the head part 3a is fitted to the axial side surface of the pipe member 1 through the curved surface 30 to attach and fix the member 3 to the pipe member 1 and other member 2 is applied to the flat surface 31 of the head part 3a through its flart surface to be attached and fixed to the pipe member 1.