PURPOSE: To provide a roll paper supply device capable of detecting the residual quantity and paper width of roll paper correctly at the same time.

CONSTITUTION: A roll paper supply device is formed of a fixed side plate disposed fixedly in the specified position of a rotary shaft 14, a free side plate disposed in either position of the rotary shaft 14 according to the paper width of roll paper 1 set between the fixed side plate and the free side plate, and a first pressing member 2 disposed on the fixed side plate side and a second pressing member 5 disposed on the free side plate side in such a way as to come in contact with both end parts of the surface of the roll paper 1 and to move around the axis of the rotary shaft 14 interlockingly with the radius-of- gyration of the roll paper 1. There are further provided an angle measuring means for measuring the angles of the first and second pressing members 2, 5 in relation to the rotary shaft 14, and a roll paper detecting means for detecting the residual quantity of the roll paper 1 from the measured angle of the first pressing member 2 and the paper width of the roll paper 1 from the measured angle of the second pressing member 5.