PURPOSE: To control fineness of yarn in a stable state by equipping a reeling machine with a fineness detector of contact friction resistance type, providing yarn, etc., before being fed to the fineness detector, with water or an aqueous solution such as chemical solution and controlling variability of contact friction resistance between the yarn and the fineness detector.

CONSTITUTION: A reeling machine 1 having a cocoon feeder 2, a reeling tank 3 connected to the cocoon feeder, a feeding end device 4 to which bave (a) reeled by the reeling tank 3 is introduced, a collecting end device 6 to which yarn obtained by combining and interlacing the bave (a) introduced to the feeding end device 4 with another yarn (b) from a yarn tube 5 is inserted and mechanism 9 to subject the yarn sent from the collecting end device 6 to kennel twisting by a pair of TSUZUMI (hand drum) wheels 7 and 8 is provided with a fineness detector 11 of contact friction type, yarn before being fed to the fineness detector 11 or the fineness detector 11 is provided with water, warm water or an aqueous solution such as chemical solution so that variability of contact friction resistance between yarn and the fineness detector is regulated to control fineness in the reeling machine 1.