Drafting device in spinning machine

The drafting device in a spinning machine for spinning a single yarn while changing the mixing proportion of two kinds of roving is provided with: a middle bottom roller and a middle top roller; a back bottom roller and a back top roller; a middle apron pair to which the first roving is supplied, the middle apron pair having a middle bottom apron wound around the middle bottom roller and a middle top apron wound around the middle top roller and being driven by the middle bottom roller with the middle top apron pressed against the middle bottom apron; and a back apron pair to which the second roving is supplied, the back apron pair having a back bottom apron wound around the back bottom roller and a back top apron wound around the back top roller and being driven by the back bottom roller with the back top apron pressed against the back bottom apron.