The blow molded preform of a laminated wall structure comprises a bulging shoulder portion, which has a diameter that widens slightly in the downward direction; a bottom shell portion for molding the bottom, which has been blow molded from the corresponding portion of parison P so as to have a widened and deformed shape; an inner overhang wall portion in any position starting from the opposite side of the neck ring and ending at the upper portion of the bulging shoulder portion, with the inner wall portion having a diameter that widens in the downward direction; and/or a radially widened connecting portion of an arced shape, which has a larger diameter than the barrel portion so that the entire bottom including the bottom shell portion takes a bulging spherical shape. With this configuration, no thick area is formed in the inner overhang wall portion on the opposite side of the neck ring and/or in the pinch-off portion.