A carriage 14 is reciprocable along a needle bed of a flat knitting machine and carries a needle cam. A pair of stitch cams 12 and 13 are adjustably supported by the carriage 14 and are disposed so as to trail behind the needle cam in alternate strokes of the carriage, respectively. An adjustment mechanism 11 includes a stepping motor 38 (FIG. 3) which adjusts the trailing stitch cam 12 or 13 not only at the beginning of the respective stroke but also during the course of the stroke itself, thereby enabling the stitch density to be varied within each row of the knitted article as well as from row to row.