To monitor paraffining without an additional means by estimating quantity in proportion to a friction coefficient of a surface of a twilling bobbin on a friction drum by continuously finding winding speed of the friction drum and the twilling bobbin in a period of a winding process.

Monitoring of paraffining is carried out by finding a friction characteristic of a surface of a twilling bobbin 17 against a friction drum 10. Absolute quantity of slipping produced on an accelerating phase between the friction drum 10 and the bobbin 17 is used as measure for it. A diameter of the bobbin 17 is computed on an inertial travelling phase without acceleration and a process of increase of the diameter of the bobbin 17 is previously computed in accordance with a value preceding the accelerating phase to find this absolute quantity of slipping. Thereafter, quantity of slipping is quantatively found from a difference between the bobbin diameter receiving distortion by slipping and an actual value. Consequently, it is possible to monitor paraffining without requiring an additional means.