Abstract: A manufacturing method includes the steps of: (A) preparing first and second sheet pieces 20a and 20b made of unvulcanized rubber; and (B) winding a long sheet 26 on a drum 6. The long sheet 26 includes the first and second sheet pieces 20a and 20b, and the second sheet piece 20b has a front edge joined to a rear edge of the first sheet piece 20a. Preferably, the step (B) includes the steps of: (B?1) joining the front edge of the second sheet piece 20b to the rear edge of the first sheet piece 20a to obtain the long sheet 26; and (B?2) feeding the sheet 26 from a servicer 4 to the drum 6 while rotating the drum 6 to wind the sheet 26 on the drum 6.