Golf club

1. A golf club comprising:

a shaft; and

a golf club head with a hollow structure fixed to a tip end of the shaft and including a face portion having a face for hitting a ball,

wherein

the golf club has a reverse flex of 110 to 160 mm, and

the face portion comprises a central thick part provided in a central region of the face portion, a toe-crown-side thin part provided on a crown-side and on a toe-side of the central thick part, and a heel-sole-side thin part provided on a sole-side and on a heel-side of the central thick part,

wherein

the central thick part has a substantially constant thickness largest in the face portion,

the toe-crown-side thin part has a substantially constant thickness smallest in the face portion,

the heel-sole-side thin part has a substantially constant thickness smallest in the face portion,

the central thick part has an area of not less than 10% and not more than 30% of the overall area of the back surface of the face portion,

the toe-crown-side thin part has an area of 8% to 20% of the overall area of the back surface of the face portion,

the heel-sole-side thin part has an area of 3% to 10% of the overall area of the back surface of the face portion,

in a front view of the golf club under its standard state in which the golf club is put on a horizontal plane at a lie angle and a loft angle which are specified for the golf club, a first straight line passing an area centroid of the toe-crown-side thin part and an area centroid of a back surface of the face portion has an angle θA of 10 to 30 degrees with respect to the horizontal plane, and a second straight line passing an area centroid of the heel-sole-side thin part and the area centroid of the back surface of the face portion has an angle θB of 36 to 40 degrees with respect to the horizontal plane,

the toe-crown-side thin part is formed in a region between two straight lines intersecting at an area centroid SG at an angle αA of not less than 60 degrees and not more than 120 degrees, and

the heel-sole-side thin part is formed in a region between two straight lines intersecting at the area centroid SG at an angle αB of not less than 60 degrees and not more than 120 degrees, wherein the area centroid SG is that of the back surface of the face portion.

2. The golf club according to claim 1 , wherein the toe-crown-side thin part and the heel-sole-side thin part have a thickness of 1.8 to 2.4 mm.

3. The golf club according to claim 1 , wherein a volume of the golf club head is 400 to 470 cc.

4. The golf club according to claim 1 , wherein the golf club head is of a wood-type.

5. The golf club according to claim 1 , wherein the area of the toe-crown-side thin part is larger than the area of the heel-sole-side thin part.

6. The golf club according to claim 1 , wherein the central thick part is composed of

a base which is generally a horizontally long oval along the contour shape of the peripheral edge of the back surface of the face portion,

an upward rib extending from an upper part of the base on its heel-side to the crown-side peripheral edge of the back surface of the face, while inclining to the heel-side, and

a downward rib extending from a lower part of the base on its toe-side to the sole-side peripheral edge of the back surface of the face, while inclining to the toe-side.

7. The golf club according to claim 6 , wherein the face portion comprises

said central thick part including the sweet spot of the club head,

said toe-crown-side thin part on the toe-side and on the crown-side of the central thick part,

said heel-sole-side thin part on the heel-side and on the sole-side of the central thick part,

a heel-side middle thickness part on the heel-side of the central thick part, and

a toe-side middle thickness part on the toe-side of the central thick part,

wherein the heel-side middle thickness part and the toe-side middle thickness part each have a substantially constant thickness smaller than that of the central thick part and larger than those of the toe-crown-side thin part and the heel-sole-side thin part.

8. The golf club according to claim 7 , wherein the thickness of the heel-side middle thickness part and the thickness of the toe-side middle thickness part are not less than 45% and not more than 85% of the thickness of the central thick part.

9. The golf club according to claim 7 or 8 , wherein the total area of the heel-side middle thickness part and the toe-side middle thickness part is not less than 10% and not more than 60% of the overall area of the back surface of the face portion.

10. The golf club according to claim 7 , wherein

on the toe-side of the central thick part, there is provided a toe-side central thickness transitional part which extends semicircularly and has a thickness that continuously decreases toward the peripheral edge of the back surface of the face portion, and

on the heel-side of the central thick part, there is provided a heel-side central thickness transitional part which extends semicircularly and has a thickness that continuously decreases toward the peripheral edge of the back surface of the face portion.

11. The golf club according to claim 7 , wherein

between the upward rib and the heel-side middle thickness part, between the upward rib and the toe-crown-side thin part, between the downward rib and the toe-side middle thickness part and between the downward rib and the heel-sole-side thin par, there is provided an outside thickness transitional part having a thickness that continuously decreases from the central thick part, and

between the heel-side middle thickness part and the heel-sole-side thin part, and between the toe-crown-side thin part and the toe-side middle thickness part, there is provided a small outside thickness transitional part that is narrower in width than the outside thickness transitional part.