A blow molding apparatus, comprising: an injection molding section for injection molding a plurality of preforms at a time; a cooling section for cooling the injection-molded preforms; a heating section for heating the cooled preforms while continuously transporting them along a transport line; and a blow molding section for blow molding the heated preforms to form hollow containers, wherein the blow molding section includes: a primary blow molding section which is equipped with a heat-treating blow mold and blow molds the preforms moved from the transport line into the heat-treating blow mold to form intermediate molded products, and a secondary blow molding section which is equipped with a final blow mold and blow molds the intermediate molded products moved from the heat-treating blow mold into the final blow mold to form hollow containers as final molded products, wherein: the injection molding section injection molds the N (N is an integer of 2 or larger) preforms at a time; the primary blow molding section divides the N preforms into n portions (n is an integer of 2 or larger), and forms the M (N/n: M is a natural number) preforms, at a time, into the intermediate molded products; and the secondary blow molding section forms the M intermediate molded products into the hollow containers at a timing when the M intermediate molded products are formed in the primary blow molding section, wherein the injection molding section injection molds the preforms in a molding time T fulfilling conditions of the following Equation: T ≥ N / M t + α where t is a heat-treating blow molding time t1, or a final blow molding time t2, whichever is longer, and α is a time during which the intermediate molded product moves from the heat-treating blow mold to the final blow mold, the amount of time to form the final molded products in the secondary blow molding section is greater than the amount of time to heat treat the intermediate molded products in the primary blow molding section, and a discharge of blow air is started after an expiration of the amount of time to heat treat the intermediate molded products and before the heat-treating blow mold is opened. an injection molding section for injection molding a plurality of preforms at a time; a cooling section for cooling the injection-molded preforms; a heating section for heating the cooled preforms while continuously transporting them along a transport line; and a blow molding section for blow molding the heated preforms to form hollow containers, wherein the blow molding section includes: a primary blow molding section which is equipped with a heat-treating blow mold and blow molds the preforms moved from the transport line into the heat-treating blow mold to form intermediate molded products, and a secondary blow molding section which is equipped with a final blow mold and blow molds the intermediate molded products moved from the heat-treating blow mold into the final blow mold to form hollow containers as final molded products, a primary blow molding section which is equipped with a heat-treating blow mold and blow molds the preforms moved from the transport line into the heat-treating blow mold to form intermediate molded products, and a secondary blow molding section which is equipped with a final blow mold and blow molds the intermediate molded products moved from the heat-treating blow mold into the final blow mold to form hollow containers as final molded products, wherein: the injection molding section injection molds the N (N is an integer of 2 or larger) preforms at a time; the primary blow molding section divides the N preforms into n portions (n is an integer of 2 or larger), and forms the M (N/n: M is a natural number) preforms, at a time, into the intermediate molded products; and the secondary blow molding section forms the M intermediate molded products into the hollow containers at a timing when the M intermediate molded products are formed in the primary blow molding section, the injection molding section injection molds the N (N is an integer of 2 or larger) preforms at a time; the primary blow molding section divides the N preforms into n portions (n is an integer of 2 or larger), and forms the M (N/n: M is a natural number) preforms, at a time, into the intermediate molded products; and the secondary blow molding section forms the M intermediate molded products into the hollow containers at a timing when the M intermediate molded products are formed in the primary blow molding section, wherein the injection molding section injection molds the preforms in a molding time T fulfilling conditions of the following Equation: T ≥ N / M t + α where t is a heat-treating blow molding time t1, or a final blow molding time t2, whichever is longer, and α is a time during which the intermediate molded product moves from the heat-treating blow mold to the final blow mold, the amount of time to form the final molded products in the secondary blow molding section is greater than the amount of time to heat treat the intermediate molded products in the primary blow molding section, and a discharge of blow air is started after an expiration of the amount of time to heat treat the intermediate molded products and before the heat-treating blow mold is opened.