PURPOSE: To simply carry out rotation control of an electric motor for driving a winding guide by counting the number of unwound weft yarns unwound from a drum in picking and issuing a rotation command of the electric motor according to the counted value thereof.

CONSTITUTION: An unwinding signal is outputted from an unwinding sensor 22 for each unwinding of weft yarn from a drum 7 by one turn in picking and the number of unwound weft yarn is then counted in a controller 20 to issue a rotation command of the number of turns corresponding to the counted value thereof to an electric motor 14. Thereby, the amount stored is kept constant.