The purpose of the present invention is to enable smooth pulling of a separator by guide members by inhibiting a phenomenon in which, when the separator is being pulled by the guide members, the separator moves in the width direction and rattles. The present invention is provided with: a step in which a separator (4) is zigzaggedly folded by being pulled by guide members (21); and a step in which, while buffer rollers (45, 46), which are disposed between support rollers (42, 43, 44) for supporting the separator (4) at midpoints located at an upstream side of a suspension roller (41) in the conveyance direction, said buffer rollers being formed so as to be capable of coming into contact with an upper surface of the separator (4) and ascending or descending to adjust the positions thereof in the vertical direction, are in a state of being stationed in a prescribed downward position, the separator (4) is suspended from the suspension roller (41) and between the guide members (21), and when the separator is being zigzaggedly folded in accordance with the movement of the guide members (21), the buffer rollers (45, 46) ascend to feed an amount of length of the separator (4), said amount being proportional to that drawin by the guide members (21).