A thread connecting device for a sewing machine cuts an upper thread which is extending between the sewing machine and one of a plurality of thread spools, and connects an end of a thread belonging to the sewing machine and an end of a thread belonging to the thread spool, in such a manner that the connected part of the threads can smoothly pass through a needle eye, whereby it is possible to supply a desired color thread with respect to the sewing machine having a single needle bar. Therefore the applicable scope of the pattern stitching may be largely widened for colored clothes or other fabrics, especially an embroidery stitching may be performed which requires many kinds of color threads.