Abstract: An apparatus for adjusting a print width in a POS printer, such as a facsimile or a printer, in which the paper is wound in the form of a roll, so that the printer can selectively use various types of paper that is be supplied thereto. The apparatus includes a paper guide, the position of which is adjustable depending on the width size of a paper to be supplied, and a contact switching means for detecting the width of the paper. The apparatus automatically detects the width of the paper with a simple operation in which the paper is inserted between or taken out of the printer, and thus automatically sets the print width to be the same as the width of the paper, so that printing is performed on the paper.