A method of molding a rubber product from a rubber compound by a molding apparatus having a kneading region. A full amount of carbon black (CB) and a full amount of process oil, together with other auxiliary materials except vulcanizing chemicals, are compounded with raw rubber to thereby knead and prepare a granular master batch (granular MB) . The rubber product is extrusion-molded and vulcanized after vulcanizing chemicals (a vulcanizing agent and a vulcanization accelerator) are quantitatively supplied into the kneading region of the molding apparatus through a material supply port while the vulcanizing chemicals are mixed with the granular MB.