PURPOSE: To carry out inspection of a joint part without necessitating the installation of a separate inspection device on the downstream of a thread joining device, by constituting the title device so that the correctness of the joint part by pulling back the joint part of threads to an inspecting device.

CONSTITUTION: When the joining of thread is completed, a thread 2 is driven out from a package 3 by the reverse revolution of a drum 4, and the slackened thread 2 is pulled into a suction tube 12 by the action of a suction flow, and a joint 11 formed in the joining of thread is pulled back to the upstream from a thread joining device 10, and allowed to pass through an inspection device 9. During the passage, the correctness of the joint part 11 is detected, and if incorrectness is detected, the joint part 11 is cut by a thread cutting device, and joining of thread is carried out and the joint part is inspected again. Thus, since inspection is carried out by pulling back the joint part 11 of the threads to the inspecting device 9 on the upstream, inspection for the joining part 11 can be carried out without necessitating a separate inspecting device 9.