PURPOSE: To prevent the mutual fusion of a plurality of sheet parisons at a place other than a predetermined place.

CONSTITUTION: In a blow mold and a blow molding method, frame bodies 30, 40 slidable in a mold pressing direction are provided to mold half bodies 10, 20 and notch parts 32, 42 having a shape approximate to the projection figure of the outer shape of a product in the mold pressing direction are provided to the end surfaces of the frame bodies 30, 40. Blow molding consists of a process introducing a plurality of sheet parisons into the opened mold half bodies, a process sliding the frame bodies 30, 40 in the mold pressing direction, a process expanding the sheet parisons in the area surrounded by the frame bodies 30, 40 toward a mold cavity by positive or negative pressure and a process closing both mold half bodies 10, 20 and mutually bonding both sheet parisons 1, 2 along a parting line under pressure and blowing air in the gap between the sheet parisons 1, 2 to perform blow molding.