Missing stitch detecting device for sewing machine

To positively and accurately detect a missing stitch without needing complicated sensitivity adjusting work even in the case of sewing any kind of cloth with different thickness and light transmission characteristics. Reflecting type photoelectric sensors for individually detecting the presence of edge parts of upper cloth and lower cloth are provided in the upper and lower positions of a throat-plate in a front position of a female mechanism in a sewing proceeding direction Y, and regression reflection tapes for reflecting projected light from the photoelectric sensors upward and downward are bonded to the upper and lower faces of a sewn cloth guide member interposed between the upper and lower cloth. A detecting means is further provided to act for determining the presence of the missing stitch of the sewn cloth by processing detection signals of both upper and lower photoelectric sensors.