PURPOSE: To form a joined yarn with high quality and to enable a knitting yarn production machine to operate at a high speed by executing joining operation, the start of the arrangement of wrapping fibers and the arrangement of core span knitting yarn onto the restarted knitting yarn.

CONSTITUTION: The knitting yarn of a certain length is drawn out of a package and is preserved in a storage unit 20. The knitting yarn is guided in the form of tense twisted yarn on the inner side of a unit formed of members for formation of the core spun knitting yarn. The fibers 1a and 1b from a draft system E are engaged with the member of a treatment block and a winding unit is restarted. The fibers 1a to be subjected to the wrapping of the core span knitting yarn are distributed onto the undercoating yarn under movement and further, the fibers 1b are distributed onto the undercoating yarn for the purpose of wrapping of the core span knitting yarn. The undercoating yarn is thereafter cut at a position parting from the storage unit 20 and a portion entering the inner side of a spinning block.