Multi-piece solid golf ball

A multi-piece solid golf ball comprising a core obtained by molding under heat a rubber composition comprising a base rubber, a filler, an organic peroxide, an antioxidant and an α,β-unsaturated carboxylic acid, and a cover of at least three layers which encases the core and in which the cover layers other than an outermost cover layer are formed primarily of a thermoplastic resin,

• wherein the core has a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) of 3.2 mm or less;
• at least one intermediate cover layer situated between an innermost cover layer and an outermost cover layer has a higher hardness than the innermost cover layer and the outermost cover layer;
• the innermost cover layer and the core have a difference in specific gravity therebetween of 0.1 or less;
• the core has a Shore D center hardness (A) which satisfies the following condition with respect to the Shore D hardness (B) of the innermost cover layer:
• A>B-10;
• the cover layers have a combined thickness of at least 3.5 mm;
• and the innermost cover layer is made of a resin composition comprising:
• 100 parts by weight of one or a mixture of
• (a) an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random copolymer, and
• (d) a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random copolymer,
• (b) from 5 to 150 parts by weight of a fatty acid or fatty acid derivative having a molecular weight of at least 228, and
• (c) from 0.1 to 10 parts by weight of a basic inorganic metal compound which is capable of neutralizing acid groups in components (a) and/or (d) and in component (b).