Golf club head

1. A hollow golf club head comprising:

a face for hitting a ball having a periphery and a face centroid, and

a face peripheral portion extending rearward of the head from the periphery of the face and provided with only two reduced-rigidity portions,

said each of the reduced-rigidity portions provided on the side of the hollow of the club head and consisting of a concave portion extending along the periphery of the face, said each of the reduced-rigidity portions having a depth in a range of from 0.2 to 1.0 mm and a width in a range of from 0.2 to 3.0 mm in a cross section perpendicular to a longitudinal direction of the concave portion, wherein

in a standard state in which the head is placed on a horizontal plane so that a centerline of a shaft axis of the head is inclined at its lie angle within a vertical plane and the face is held at its loft angle,

the reduced-rigidity portions consist of one toe-side reduced-rigidity portion provided on the toe side of the face centroid and one heel-side reduced-rigidity portion provided on the heel side of the face centroid, and

when the head in the standard state is viewed from a direction of a normal of the face centroid,

said toe-side reduced-rigidity portion has a center point P 1 of its length located higher at the toe side of the face centroid, wherein an angle θt of a first straight line connecting the face centroid with the center point P 1 of the toe-side reduced-rigidity portion with respect to the horizontal plane is in a range of from 30 to 45 degrees, and

the heel-side reduced-rigidity portion has a center point P 2 of its length located lower and the heel side of the face centroid, wherein an angle θh of a second straight line connecting the face centroid with the center point P 2 of the heel-side reduced-rigidity portion with respect to the horizontal plane is in a range of from 30 to 50 degree.

2. The golf club head according to claim 1 , wherein the head comprises:

a cup-shaped face member having the face and a flange portion which extends rearward of the head from the periphery of the face to constitute the face peripheral portion, and

a head main body fixed to a rear side of the face member.

3. The golf club head according to claim 1 , wherein said each reduced-rigidity portion has a longitudinal length in a range of from 5 to 60 mm.

4. The golf club head according to claim 1 , wherein said reduced-rigidity portions has a smooth curved shape in a cross section perpendicular to the longitudinal of the concave portion.

5. The golf club head according to claim 1 , wherein said reduced-rigidity portions are arranged on a corner formed between the face peripheral portion and the face, in a cross section perpendicular to the longitudinal direction of the concave portion.

6. The golf club head according to claim 1 , wherein the face peripheral portion is an area within 10 mm from the periphery of the face to the rearward of the head.

7. The golf club head according to claim 1 , wherein the angle θt is smaller than the angle θh.

8. The golf club head according to claim 1 , wherein said toe-side reduced-rigidity portion and said heel-side reduced-rigidity portion have the same longitudinal length.

9. The golf club head according to claim 1 , wherein the face peripheral portion has a flat exterior surface so that each of said toe-side reduced-rigidity portion and said heel-side reduced-rigidity portion has a small thickness.