To prevent a compressional stress and an elongation from being applied to the whole axially expansion of a carcass after the completion of the setting of a core by a method wherein the initially set diameter for assembling the carcass is made to be nearly coincident with the diameter to be expanded.

A negative pressure container, to which an exhayst pump is connected, is arranged in the periphery of a drum so as to suck a carcass 10 from the periphery of the drum 1 by developing a vacuum in the negative pressure container in order to fix the carcass 10. A sleeve 3 is assembled on segments 2 under a shrunk state so as to shrink a drum further more than necessary for sending a bead core 111 for positioning. Under the condition that the carcass, which contacts without folds with the drum 1, is shrunk enough, the bead core 111 is brought into its correct position on the drum 1. When the drum 1 is expanded, the diameter of the drum 1 is matched to the inner diameter of the bead core 111 so as to press the bead core 111 and the flattened carcass 10 with each other. Finally, the diameter of the drum 1 is again reduced to a smaller one.