The present invention relates to an apparatus for monitoring the yarn or yarns in a carpet making machine or the like, a so-called tufting machine, in which the yarn or yarns are applied on a bed material, e.g. a bed weft, during movement of the yarn or yarns from a yarn magazine, e.g. a creel with a number of yarn bobbins (B) on a number of posts (S) in one or more storeys, to the bed material each through its transparent or translucent tube (R), e.g. a hose, at least one light emitter (4) and one light receiver (6) being positioned at each tube (R) for yarn which is to be in motion and to be monitored, and the light receivers (6) are rehearsed to convert received light into an electric signal which is connected to an electronic circuit for triggering an alarm and possible stoppage of the machine when the electric signal indicates that the yarn in its tube (R) is not in motion.