Preform, synthetic resin container, and method for manufacturing synthetic resin container

A synthetic resin preform that includes an outer body and an inner body laminated on an inner surface of the outer body and that is used for stretch blow molding, the synthetic resin preform comprising:

• a tubular mouth;
• a trunk below the mouth;
• and
• a bottom that closes a lower end of the trunk, wherein
• in the mouth, the inner body includes a large-diameter portion at an upper end thereof, and a small-diameter portion continuously extending below the large-diameter portion via a connecting portion,
• in the mouth, the outer body includes an ambient air introduction hole passing through the outer body, and a neck ring within a height range of the small-diameter portion,
• the inner body is made of a crystalline resin, and a crystallized region is in part of the inner body, the crystallized region having a higher degree of crystallization than other regions,
• the crystallized region has an upper end that is within a height range extending between an upper end of the connecting portion and an upper end of the neck ring, and
• the crystallized region has a lower end that is below the neck ring,
• the ambient air introduction hole is within a height range of the small-diameter portion and above the upper end of the neck ring, and
• the upper end of the crystallized region is at a height position between a lower end of the ambient air introduction hole and above the upper end of the neck ring.