A tire building drum comprises a main drum shaft, a pair of movable bodies, approaching-separating means for moving these movable bodies in opposite directions, plural bead lock segments movably supported by each of the movable bodies in a radial direction, enlarging-contracting means for synchronously moving these bead lock segments in the radial direction, a seal member, a hollow cylindrical body and plural turnup fingers, wherein the seal member comprises an inner elongated portion extending inward from its base end part airtightly fixed to the movable body in the axial direction and an outer elongated portion extending outward from an inner end of the inner elongated portion in the axial direction.