A two or three piece golf ball in which a boundary surface between concentric solid layers has a projection formed on the surface of a concentric solid layer having a high hardness such that the projection extends along an approximate normal direction, a depression corresponding to the projection is formed in the surface of a concentric solid layer having a low hardness, and the concentric solid layer having a high hardness and the concentric solid layer having a low hardness are joined together such that the projection is inserted into the depression. A golf ball comprising a two-layer solid core is composed of a low-hardness inner core and a high-hardness outer core joined around the low-hardness inner core. A projection is formed on the inner surface of the high-hardness outer core such that the projection extends along an approximate normal direction, while a depression corresponding to the projection is formed in the outer surface of the low-hardness inner core, and the low-hardness inner core and the high-hardness outer core are joined together such that the projection is inserted into the depression.