To prevent core misalignment when performs are stretched during blow molding, provided is a blow molding device that blow molds a preform into a container in a forming mold. The blow molding device includes a support pin that is disposed in the forming mold. The support pin includes a head that supports a bottom portion of the preform, and a shaft that is connected to the head and that is displaceable upward and downward in a direction of an axis of the preform. The head is provided, at one end thereof supporting the bottom portion of the preform, with a concave portion for receiving at least a part of the bottom portion.