PURPOSE: To provide the titled quality control where a doffing truck traveling between the winder of a false twister and peg stand is fitted with a yarn quality-measuring instrument, thus making a truck for moving a measuring device to the measuring area for each winder unnecessary.

CONSTITUTION: A doffing truck 25 is made to travel on a rail 24 through rollers 26 between a peg stand 20 and winder 3. The head of said truck 25 is fitted with a quality-measuring instrument 46, and yarn quality is determined at approximately the same time as that of the doffing operation using a device 60 fitted as required at the tip of the arm 47, the resulting data being transmitted to a quality control equipment 66, thus obtaining individual quality control information corresponding to each wound package.