PURPOSE: To perfectly remove a yarn wound on the outer periphery of the core tube, etc. of a package by allowing a slab catcher to detect the sucked yarn sucked into a suction mouth and setting the reversal time of the package longer than a prescribed time for the preceding processes, in the next yarn relaying.

CONSTITUTION: When double yarn is sucked into a suction mouth 7 during the yarn relaying operation, a slab catcher 4 detects said suction, and in the next yarn relaying operation, the yarn wound onto the outer periphery of a core tube, etc. of a package 6 can be surely removed by setting the reversal time of the package 6 longer than a prescribed time for the preceding processes.