A preform having an inverted truncated conical bottom section is used. The inclined inner surface of a bottle bottom surface-forming portion of the bottom section is formed into a gently curved convex surface that extends from the lower portion of a bottle bottom edge-forming portion of the bottom section to a curved portion in the lower portion of the bottom section so that the thickness of the bottle bottom surface-forming portion is greater than the thickness of the barrel section of the preform and the thickness of the bottle bottom edge-forming portion. The increase in thickness of the bottom section improves the efficiency of stretching the bottom section, and the circumferential wall of the bottom section can thereby be efficiently stretched. This allows a reduction in weight (thickness) of the bottom surface section of a stretch blow molded bottle, and a reduction in weight of the bottle is thereby achieved.