A joint (20) joins a plate member (26) with a preform (22), wherein an inclined part (28), which is inclined relative to a surface that is orthogonal to the direction in which a tensile load is applied to the plate member (26), is formed on a surface (25) that joins with the preform (22). Moreover, an indented part (38) corresponding to the shape of the inclined part (28) is formed on the preform (22) so that the inclined part (28) of the joint (20) is embedded into the indented part (38). The joint (20) is embedded in and bonded to the preform (22).