PURPOSE: To piece a two ply yarn under a condition suitable for the properties of each single yarn thereof by independently adjusting the inner diameters and compressed air-jetting angles of the yarn end-untwisting pipe and twist- piecing nozzle of each air type piecing member for separately piecing each single yarn.

CONSTITUTION: A two ply yarn is divided into two single yarns, which are conducted into piecing members 1 prepared only for the single yarns on the basis of the judged kinds of the single yarns, respectively. The inner diameters and compressed air jetting angles of the yarn end-untwisting pipes 2 and twist- piecing nozzles 3 of the piecing member 1 are independently adjusted in response to the physical properties of the single yarns to be treated, respectively.