PURPOSE: To enable to accurately discriminate the side of a paper even when a printed part or the like is present on the paper, by a method wherein the presence or absence of a paper is discriminated on the basis of detection signals in a plurality of paper-feeding condictions, when detecting the size of a cut recording paper.

CONSTITUTION: When a paper-feeding command is fed from a main controlling circuit to a printer, a driving motor is energized, and a platen 2 is rotated until a detection signal from a paper detector 8a becomes "1", thereby feeding the recording paper 1. When the paper-feeding operation is completed, a CPU takes up detection signal D1n from the paper detectors 8aW8d, and store them into an RAM. Then, after further feeding the paper 1 by a predetermined amount to change the paper-feeding condition, detection signals D2n from the detectors 8aW8d are again stored into the RAM, and when the paper is of the A4 size, for example, the logical sum of two detection signals from the detector 8c is calculated, and when the calculation result is "0", the paper 1 is discriminated as being not larger than the designated size, and an error display is accomplished.