In order to control the movement of a label web to be imprinted past the printing head of a thermal printer, or the like, the label web carries optically detectable marks at predetermined intervals therealong. The label web is comprised of label pieces adhesively secured to an underlying supporting web. An optical sensor for detecting the marks on the label web is disposed on a label holding member which is hinged to a supporting base, so that the label web is fed past the supporting base and is pressed thereagainst by the label holding member. Holes located on the supporting base at opposite sides of the label web help remove any adhesive material that is emitted from the sides of the label web. The support base has guiding lands for guiding the movement of the label web. The operation of the printer and of the label feed device is controlled by the optically sensed marks on the web.