A fastener includes a head portion, a leg portion, and an easily deformable portion. The head portion is formed in a cylindrical shape with an oval shape in an axial view. The leg portion has one end portion in an axial direction that is connected to a back surface of the head portion. The leg portion is formed in a hollow cylindrical shape with an oval shape in the axial view whose minor axis direction is the same as a minor axis direction of the oval shape of the head portion. The easily deformable portion is provided to a pair of major-axis leg portions which are portions crossing a major axis in the leg portion.