A head 2 is hollow. The head 2 has a sole part 8. The sole part 8 has a groove forming part k1 having a recessed outer surface g1 and a protruding inner surface s1. The sole part 8 has a first groove forming part k1 and a second groove forming part k1. The first groove forming part k1 and the second groove forming part k1 have a front-back directional length. A distance between the first groove forming part k1 and the second groove forming part k1 in a toe-heel direction is wider toward a back of the head. Preferably, the first groove forming part k1 and the second groove forming part k1 exist on a back of a face surface 13. Preferably, the sole part 8 has a connecting groove part r1. The connecting groove part r1 is formed by connecting a front end of the first groove forming part k1 to a front end of the second groove forming part k1 with each other.