In an embodiment, a neck mold assembly includes N rows of holding plates, each of the N rows of holding plates holding a plurality of neck molds. The neck mold assembly also includes a supporting-mechanism that supports the N rows of holding plates. The supporting mechanism includes at least one reinforcement shaft that is provided along a row direction of the N rows of holding plates, and two first securing sections that are secured at either end of the at least one reinforcement shaft. Each of the N rows of holding plates has at least one first through-hole that receives the at least one reinforcement shaft.