After a cyclopentadiene compound and a vinyl aromatic compound are thermally polymerized, the obtained copolymer is subjected to a hydrogenation reaction to form a hydrogenated product. After most of the hydrogenation solvent is separated by a solvent evaporation tank from the hydrogenated product, an additive separately prepared by dissolving an antioxidant is added to the hydrogenated product to form a mixture. While the hydrogenation solvent is a naphthenic solvent, the additive is prepared by dissolving the antioxidant in an aromatic additive solvent having the same carbon atoms as those of the hydrogenation solvent. Then, the low-molecular-weight component as well as the remaining hydrogenation solution and the additive solvent are separated by a thin-film evaporator from the mixture. The obtained molten resin is pelletized to produce hydrogenated petroleum resin pellets. The time for uniformly blending the antioxidant can be shortened.