Abstract: A blow molding device including: an injection molding unit manufacturing a bottomed preform made of resin; a blow molding unit; a support part supporting the preform; and a conveying unit conveying the support part to the blow molding unit, wherein the blow molding unit includes: a first mold for performing a first step of subjecting the preform to heat-set blowing at a first temperature; a second mold for performing a second step of blow-molding an intermediate molded article, which has been blow-molded by the heat-set blowing, at a second temperature lower than the first temperature, thereby manufacturing a container; and a movement unit capable of moving the first mold and the second mold relative to the support part so as to perform the first step and the second step continuously.