The ridge part T projecting from an interior surface of an opening and closing cover 3 of a printer 1 is provided at part of a head 3b that make contact with a mountless label continuous body P including an adhesive agent layer on one surface thereof. The head 3b is located at a free end of the opening and closing cover 3. A third ridge part T3 is provided on a third surface S3, which is located in vicinity of an intersecting line between a first surface S1 and a second surface S2. The third ridge T3 has a longer projecting length than a ridge part T1 projecting from the first surface S1, and has a longer projecting length than a ridge part T2 projecting from the second surface S2.