A sewing machine for performing sewing on a sewing workpiece based on sewing pattern data, the sewing machine comprising: a detector configured to detect a used length of an upper thread per stitch or per plurality of stitches during sewing operation of the sewing machine, a processor, a memory, and an output device (16, 30, 31), characterized in that: the processor is configured to calculate, during the sewing operation of the sewing machine, a stitch tightness index per sewn stitch or per plurality of sewn stitches based on: (i) a stitch length per stitch or per plurality of stitches defined by the sewing pattern data and (ii) a fabric thickness of the sewing workpiece and (iii) detected data of the used length of the upper thread per stitch or per plurality of stitches; the memory is configured to store, for a plurality of sewn stitches, the calculated stitch tightness index per sewn stitch or per plurality of sewn stitches in association with a finished sewn product, the memory storing a plurality of the stitch tightness indexes for the plurality of sewn stitches; and the output device (16, 30, 31) is configured to output information notifying the calculated stitch tightness index per sewn stitch or per plurality of sewn stitches. a detector configured to detect a used length of an upper thread per stitch or per plurality of stitches during sewing operation of the sewing machine, a processor, a memory, and an output device (16, 30, 31), characterized in that: the processor is configured to calculate, during the sewing operation of the sewing machine, a stitch tightness index per sewn stitch or per plurality of sewn stitches based on: (i) a stitch length per stitch or per plurality of stitches defined by the sewing pattern data and (ii) a fabric thickness of the sewing workpiece and (iii) detected data of the used length of the upper thread per stitch or per plurality of stitches; the memory is configured to store, for a plurality of sewn stitches, the calculated stitch tightness index per sewn stitch or per plurality of sewn stitches in association with a finished sewn product, the memory storing a plurality of the stitch tightness indexes for the plurality of sewn stitches; and the output device (16, 30, 31) is configured to output information notifying the calculated stitch tightness index per sewn stitch or per plurality of sewn stitches. the processor is configured to calculate, during the sewing operation of the sewing machine, a stitch tightness index per sewn stitch or per plurality of sewn stitches based on: (i) a stitch length per stitch or per plurality of stitches defined by the sewing pattern data and (ii) a fabric thickness of the sewing workpiece and (iii) detected data of the used length of the upper thread per stitch or per plurality of stitches; the memory is configured to store, for a plurality of sewn stitches, the calculated stitch tightness index per sewn stitch or per plurality of sewn stitches in association with a finished sewn product, the memory storing a plurality of the stitch tightness indexes for the plurality of sewn stitches; and the output device (16, 30, 31) is configured to output information notifying the calculated stitch tightness index per sewn stitch or per plurality of sewn stitches.