To provide an almost constant back tension on a paper drawn out from a rolling part always even when the diameter of machine glazed paper is changed by a simple adjustment mechanism.

The position of a shaft 3a of a potentiometer 3 corresponding to the position of an arm 2 when machine glazed paper 1 with a fixed diameter is set, is determined to be a reference phase. When the diameter of the roll paper 1 is changed corresponding to the consumption of the roll paper 1, the arm 2 makes the angular changes around the shaft 3 of the potentiometer 3 and the phase of the shaft 3a of the potentiometer 3 is changed. Accordingly, the diameter of the roll paper 1 can be detected by the difference of the output voltage value of the potentiometer 3 and the voltage value of the potentiometer 3 when the shaft 3a of the potentiometer 3 is in the reference phase. The electric current corresponding to the diameter of the roll paper 1 is supplied to a motor connected to a gear so that a constant back tension is given always on the paper drawn out from the rolling part of the machine grazed paper 1.