PURPOSE: To discriminate the empty bobbin from the bobbin having residual yarn correctly, and decrease the detection miss, by detecting the bobbin according to the displacement of the piece for detecting residual yarn when the bobbin having yarn layers is passed through the transfer path of the bobbin.

CONSTITUTION: The sensor S2 of the discriminator A is furnished with the detection bar 6 placed close to the bobbin (b) transferred by the conveyor 3. When the tilt of the detection bar 6 is detected, the tray 1 is passed without being stopped. The sensor S3 is furnished with the residual yarn detecting piece to detect the presence of even a small residual yarn at a part of the bobbin (b), and the detection piece 120 is tilted and the bobbin is discriminated in the course of the upward motion of the tilting member when there is a yarn layer Y2 on the bobbin (b).