Abstract: A blow molding method for manufacturing a container equipped with a receptacle divided by a partition wall, wherein the partition wall is formed in a preform, which is in general fabricated by injection molding, the preform is arranged in a blow molding die, and blow molding is performed to the preform in a molding process which is conducted two times, so that a container product has constant partition walls overall. The blow molding method includes forming a preform having a receptacle divided by the partition wall, arranging the preform in a blowing mold and initially blow molding the same via a first blowing so as to impart a certain shape, and secondarily blow molding the resultant via a second blowing so as to impart a shape corresponding to that of the blowing mold.