A stem 8 has the following elements made from FRP: an upper outer shell 4U, a main structure upper half 3U, a main structure lower half 3L, and a lower outer shell 4L when the stem is placed in a flat state. The elements are integrated into one piece by stacking the elements and applying heat and pressure to melt resins impregnated in the FRP structural elements. Each outer shell is a curved prepreg sheet formed by impregnating carbon fibers arranged at angle of ±45 degrees with a thermoplastic resin, and each upper and lower halve is an evenly stacked part in which prepreg sheets are stacked. Overlapping section 5 of the upper and lower outer shells are formed such that the left and right portions of a main structure 3 formed by integrating the upper and lower halves 3U, 3L does not have a stepped outer surface.
