A mold pin fixed to a tread mold for a tire tread and forming a stud hole is disclosed. The mold pin is provided at one end of its main shaft portion with an expanded portion having a larger outer diameter. The expanded portion comprises a supporting part formed integrally with the main shaft portion, and an outer-shell part disposed on the outer surface of the supporting part to define the maximum outer diameter of the expanded portion. When a force directed from the main shaft portion toward the expanded portion is applied to the outer-shell part, the outer-shell part is moved so as to reduce the maximum outer diameter.