To increase the capacity of a drum for molding a tire by reducing a load applied to an expansion/contraction means 55.

Since an inside extension part 58b which extends toward the inside in the axial direction and an outside extension part 58c which extends toward the outside in the axial direction and in which the tip part covers a bead lock segment 44 are formed in a seal member 58, when the segment 44 is moved outside in the radius direction, and the tip part of the outside extension part 58c is expanded, the inside and outside extension parts 58b, 58c are only deformed to make their cross sections open in a V-shape so that resistance is reduced during the expansion.