To accurately cut a ply for a tire. It is a cutting device 1 for cutting a ply 10 for a tire in which a plurality of cords 12 parallelly arranged at fixed pitches are coated with an unvulcanized topping rubber 10. It has a pitch increasing means 2 for increasing the pitches of the cords 12 by pressing the ply 10 from a second surface 10b side to a first surface 10b side of the ply 10 so as to stretch the ply 10 toward the first surface 10a side; and a ply cutting means 3 disposed on the first surface 10a side of the ply 10, for cutting the stretched portion of the ply 10 along the cords 12.