To prevent core misalignment when performs are stretched during blow molding, provided is a blow molding device 10a that blow molds a preform 20 into a container in a forming mold. The blow molding device 10 includes a support pin P1 that is disposed in the forming mold. The support pin P1 includes a head 13 that supports a bottom portion 24 of the preform 20, and a shaft 14 that is connected to the head 13 and that is displaceable upward and downward in a direction of an axis O 2 of the preform 20. The head 13 is provided, at one end thereof supporting the bottom portion 24 of the preform 20, with a concave portion 13c for receiving at least a part of the bottom portion 24.