the sweet spot may be identical or different the radius of the central part 17 is preferably about 3 0 mm or greater further preferably about 3 5 mm or greater also the radius of the central part 17 is preferably about 6 mm or less further preferably about 5 mm or less by making the radius of the central part 17 in this range the weight of the face part can be kept low the shape of the central part 17 is not limited to the circular shape shown in fig2 and may be elliptical rectangular or polygonal such as tetragonal pentagonal or hexagonal the thickness of the central part 17 is preferably about 3 4 mm or greater further preferably about 3 6 mm or greater also the thickness of the central part 17 is preferably about 4 0 mm or less further preferably about 3 8 mm or less by making the thickness of the central part 17 in this range the restitution coefficient of the face part can be kept in the range specified by the rule the major axis of the ellipse indicated by the line 13 is inclined so that the toe 3 side thereof shifts to the crown side and the heel 2 side thereof shifts to the sole side the reason for this is as described.