In a head, a center vertical cross section passing through a face center satisfies the following (a) and (b):
(a) when a boundary point between an inner surface of a crown portion and an inner surface of a face portion is defined as a CF inner surface boundary point, a curvature radius of a head inner surface at the CF inner surface boundary point is 6.0 mm or greater and 10.0 mm or less, and the head thickness at the CF inner surface boundary point is 2.0 mm or greater; and

(b) when a spot located 10 mm apart from the CF inner surface boundary point toward the crown side is defined as a spot C10, the head thickness reduces gradually from the CF inner surface boundary point to the spot C10, and the head thickness at the spot C10 is 1.0 mm or less.