Abstract: Blow-molding molds 10 and 20 having parison shutters 31 and 32 for preventing an inflation of the parison 3 toward the outside of the molds 10 and 20 are used in a blow-molding method of the present invention. In other words, a closed space for preventing the parison 3 from inflating out of the molds 10 and 20 are formed by the parison shutters 31 and 32 and a predetermined air is secured in the parison 3 in a frame clamping step (B). In the subsequent mold clamping step (C), the pressure inside the parison 3 starts to be increased when the molds 10 and 20 press the parison 3, so that the parison 3 can be continuously in contact with the die design surface 11. Accordingly, since the parison 3 can be uniformly contracted by cooling, molding failure such as streaks and uneven pattern transfer can be avoided, thus obtaining a blow-molded product having good appearance.