PURPOSE: To make the filament speed follow the target value and stabilize the filament speed, by using apparatues for sensing the running speed provided on discs rotating in contact with running cocoon filaments reeled from a reeling part, determining the filament speed difference between the reeling positions, and controlling the reeling speed by the obtained values.

CONSTITUTION: Rotating discs 3 ane 3' rotating in contact with running cocoon filaments 1' and 1" reeled from a reeling and opening part 1 are provided with eccentric sintered permanent magnets 2 and 2' at the rear sides thereof and coils 4 and 4' at the rears opposite to the magnets 2 and 2' to give electric pulse signals in proportion to the number of revolutions of the respective discs 3 and 3'. The signals are counted for a given time to determine the running speeds of the cocoon filaments 1' and 1" by an apparatus 12. The difference between the filament speeds at the time is compared with the speed previously set in an apparatus 14 by an apparatus 13, and the signals of the compared values are sent to an electric circuit of a reversible motor 18. The rotation of the reversible motor 18 is transmitted to a speed controlling part of a speed change gear device 19 linked to a motor 24 to control the rotational speed of a sprocket 26. The rotational speed is then transmitted to a rotating shaft 27 of small reels 11 and 11' to reel the filaments at the constant target speed regradless of the increase in the outside diameter of raw silk wound onto the small reels 11 and 11'.