When a label printer detects the paper width, the paper width detection operation scans the transportation path in the paper width direction by the paper width detector not once but twice, and conveys the recording medium transportation distance L, which is longer than the gap length of the gap between labels and is shorter than the label length of each label, between the first and second paper width detection operations. Of the two positions detected as the left edge of the recording medium in the first and second detection operations, the position that is farthest left is used. Likewise, of the two positions detected as the right edge of the recording medium in the first and second detection operations, the position that is farthest right is used.