PURPOSE: To determine positioning of molding fixture corresponding to a target spindle to be doffed independently of length of a sliding member, by deciding the position in the direction of guide rail of the holding fixture of a doffer stopped at a doffing position in front of a frame in such a way that the holding fixture is sent to given position by a device to determine positioning.

CONSTITUTION: The doffer 26 arranged in front of the frame 1 is provided with the device 38 for determing positioning of holding fixture which is to be engaged with the sliding member 15 in a state wherein the doffer is stopped at the doffing position, and decides the position in the direction of the guide rail 6 of the holding fixture 16 corresponding to at least a spindle to be doffed in such a way that the holding fixture is set at a given position based on the doffer. Before doffing operation by the doffer is carried out, the holding fixture 16 of bobbin transfer device corresponding to a target spindle to be doffed is moved to a corrected position of given position suitable for doffing.