A core having a center, and a mantle layer comprising a thermoplastic resin composition is provided. Next, a reinforcing layer including a thermosetting resin composition is formed on the surface of this core to obtain a spherical body 40. Next, this spherical body 40 is covered by two pieces of half shell 46. Next, the spherical body 40 and the half shells 46 are placed into a mold 32. Next, the mold 32 is clamped at a velocity of 0.01 mm/sec or greater and 1.0 mm/sec or less. The thermoplastic resin composition of the half shell 46 is heated while being compressed in the spherical cavity to result in flow. This thermoplastic resin composition is hardened to give a cover having a thickness of 0.1 mm or greater and less than 0.7 mm. The difference (T−Fc) between the molding temperature T and the incipient fluidization temperature Fc of the thermoplastic resin composition of the cover is 0° C. or greater and 30° C. or less.