Golf club head

1. A wood type golf club head including, a crown portion on an upper side of the head, a sole portion on the lower side of the head and a face portion between the crown portion and the sole portion, wherein

a plurality of grooves arrayed in a vertical direction of the face portion are formed in the face portion,

a depth of the plurality of grooves is less than 0.025 mm, and

when pitches between grooves, among the plurality of grooves, that are adjacent in the vertical direction of the face portion are represented by P 1 , P 2 , . . . , P n sequentially from an upper side to a lower side of the face portion

P 1 ≧P 2 ≧ . . . ≧P n , and

P 1 >P n ,

the face portion includes a lower area, a central area, and an upper area,

letting H be a height of the face portion in the vertical direction,

the lower area is an area of H×0.3 from a lower end of the face portion,

the central area is an area of H×0.7 from an upper end of the lower area, and

the upper area is an area from the upper end of the central area to the upper end of the face portion, and

when a surface roughness of the face portion is measured as an arithmetic mean roughness Ra using an average line in the vertical direction,

an average value of the arithmetic mean roughness Ra of the lower area is 2 μm or more,

the average value of the arithmetic mean roughness Ra of the central area is not less than 1 μm and less than 2 μm, and

the average value of the arithmetic mean roughness Ra of the upper area is less than 1 μm.

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

1 mm≦P 1 ≦5 mm, and

100 μm≦P n ≦200 μm.

3. The golf club head according to claim 1 , wherein the plurality of grooves are formed by laser machining.

4. The golf club head according to claim 1 , wherein the face portion includes an impact area, and

there are no scorelines in the impact area.

5. The golf club head according to claim 1 , wherein each of the plurality of grooves comprises a straight groove extending in a direction perpendicular to the vertical direction.

6. The golf club head according to claim 1 , wherein the grooves are not formed in the upper area.

7. The golf club head according to claim 1 , wherein P 1 >P k >P n (1<k<n).

8. The golf club head according to claim 1 , wherein P 1 >P j >P k >P n (1<j<k<n).

9. The golf club head according to claim 1 , wherein P 1 >P 2 > . . . >P n .

10. A wood type golf club head including, a crown portion on an upper side of the head, a sole portion on a lower side of the head and face portion between the crown portion and the sole portion, wherein

a plurality of grooves arrayed in a vertical direction of the face portion are formed in the face portion,

a depth of the plurality of grooves is less than 0.025 mm,

pitches between grooves, among the plurality of grooves, that are adjacent in the vertical direction of the face portion change such that a surface roughness of the face portion rises from an upper side to a lower side,

the face portion includes a lower area, a central area, and an upper area,

letting H be a height of the face portion in the vertical direction,

the lower area is an area of H×0.3 from a lower end of the face portion,

the central area is an area of H×0.7 from an upper end of the lower area, and

the upper area is an area from the upper end of the central area to the upper end of the face portion, and

when a surface roughness of the face portion is measured as an arithmetic mean roughness Ra using an average line in the vertical direction,

an average value of the arithmetic mean roughness Ra of the lower area is 2 μm or more,

the average value of the arithmetic mean roughness Ra of the central area is not less than 1 μm and less than 2 μm, and

the average value of the arithmetic mean roughness Ra of the upper area is less than 1 μm.