To provide a hollow spherical body from a billet formed by cutting, etc., with a simple, rational and economical method.

A billet of a starting member is formed into a blank 12 provided with a first half part 13 having an outer wall of the shape corresponding to a part of a sphere, and a second half cylindrical part having an outer wall 14 and an inner wall 15 which are concentrically arranged with a clearance opened upward, and an intermediate plate to cover a hole in the axial direction on the inner side of the inner wall by a lower part of the inner wall. The outer wall 14 of a second half part which is a rest of the blank is formed to the shape corresponding to a part of the sphere continuous to the part 13. Finally, a free end of the outer wall 14 is brought into close contact with a free end of the inner wall 15 to cover the clearance with an upper end part and form a cavity 20, and the intermediate plate 17 is removed to make the hole on the inner side of the inner wall a continuous through hole.