Golf ball

1. A golf ball comprising a spherical core, a mid layer positioned outside the core, and a cover positioned outside the mid layer, wherein

the core includes an inner core comprising a polybutadiene composition, a mid core positioned outside the inner core comprising a polybutadiene composition, and an outer core positioned outside the mid core comprising a polybutadiene composition,

the mid layer includes an inner mid layer and an outer mid layer positioned outside the inner mid layer,

a JIS-C hardness H(C) at a point C present outward from a boundary between the inner core and the mid core in a radius direction by 1 mm is equal to or greater than a JIS-C hardness H(B) at a point B present inward from the boundary between the inner core and the mid core in the radius direction by 1 mm,

a JIS-C hardness H(E) at a point E present outward from a boundary between the mid core and the outer core in the radius direction by 1 mm is equal to or greater than a JIS-C hardness H(D) at a point D present inward from the boundary between the mid core and the outer core in the radius direction by 1 mm,

when an angle (degree) calculated by (Formula 1) from a thickness Y (mm) of the mid core, the hardness H(C), and the hardness H(D) is defined as an angle α and an angle (degree) calculated by (Formula 2) from a thickness Z (mm) of the outer core, the hardness H(E), and a JIS-C hardness H(F) at a point F located on a surface of the core is defined as an angle β:

α=(180°/π)* a tan[{ H ( D )− H ( C )}/Y]  (Formula 1); and

β=(180°/π)* a tan[{ H ( F )− H ( E )}/Z]  (Formula 2),

the angle α is equal to or greater than 0°,

a difference (α−β) between the angle α and the angle β is equal to or greater than 0°, and

a Shore D hardness Hm 2 of the outer mid layer is greater than a Shore D hardness Hm 1 of the inner mid layer, and

the composition of the inner core, midcore, and outer core are different.

2. The golf ball according to claim 1 , wherein the angle β is equal to or greater than −20° but equal to or less than +20°.

3. The golf ball according to claim 1 , wherein

a ratio (Y/X) of the thickness Y of the mid core relative to a radius X of the inner core is equal to or greater than 0.5 but equal to or less than 2.0, and

a ratio (Z/X) of the thickness Z of the outer core relative to the radius X is equal to or greater than 0.5 but equal to or less than 2.5.

4. The golf ball according to claim 1 , wherein

a ratio (S 2 /S 1 ) of a cross-sectional area S 2 of the mid core relative to a cross-sectional area S 1 of the inner core on a cut surface of the core that has been cut into two halves is equal to or greater than 1.0 but equal to or less than 8.0, and

a ratio (S 3 /S 1 ) of a cross-sectional area S 3 of the outer core relative to the cross-sectional area S 1 on the cut surface of the core is equal to or greater than 2.5 but equal to or less than 12.5.

5. The golf ball according to claim 1 , wherein

a ratio (V 2 /V 1 ) of a volume V 2 of the mid core relative to a volume V 1 of the inner core is equal to or greater than 2.5 but equal to or less than 20.0, and

a ratio (V 3 /V 1 ) of a volume V 3 of the outer core relative to the volume V 1 is equal to or greater than 10.0 but equal to or less than 57.0.

6. The golf ball according to claim 1 , wherein a difference (Hm 2 −Hm 1 ) between the hardness Hm 2 and the hardness Hm 1 is equal to or greater than 10.

7. The golf ball according to claim 1 , wherein a sum (Tm 1 +Tm 2 ) of a thickness Tm 1 of the inner mid layer and a thickness Tm 2 of the outer mid layer is equal to or greater than 0.8 mm but equal to or less than 2.2 mm.

8. The golf ball according to claim 1 , wherein a thickness Tm 2 of the outer mid layer is greater than a thickness Tm 1 of the inner mid layer.

9. The golf ball according to claim 1 , wherein

the hardness Hm 1 is equal to or greater than 30 but equal to or less than 65, and

the hardness Hm 2 is equal to or greater than 55 but equal to or less than 80.