Near-end of roll detecting apparatus for detecting near-end of roll of recording medium, and printer

A near-end of roll detecting apparatus for a roll of recording medium, comprising:

• a recording medium support unit that supports an outer circumferential surface of the recording medium that is biased downward in a vertical direction by the weight of the recording medium, such that a position of a center of the recording medium moves on a straight-line trace, associated with consumption of the recording medium;
• a displacement sensing unit that is provided at a position facing a predetermined position at a side face of the recording medium and senses displacement per unit time at the predetermined position at the side face of the recording medium when the recording medium is rotated by being pulled out of the recording medium support unit, associated with the consumption of the recording medium, wherein the rotational axis of the roll is perpendicular to the side face;
• and
• a calculating unit that calculates based on the displacement sensed by the displacement sensing unit, a radius of the recording medium at the time the displacement sensing unit senses the displacement.