Provided is a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer, and a cover having a plurality of dimples. The core has a hardness which gradually increases from a center to a surface thereof, the hardness difference in JIS-C hardness units between the core center and the core surface being at least 15 and, letting (I) be the average value for cross-sectional hardnesses at a position about 15 mm from the core center and at the core center and letting (II) be the cross-sectional hardness at a position about 7.5 mm from the core center, the hardness difference (I)−(II) in JIS-C units being not more than ±2. The envelope layer, intermediate layer and cover have hardnesses which satisfy the condition: cover hardness>intermediate layer hardness>envelope layer hardness.