A flatbed knitting machine comprising a variable stitch device, wherein the variable stitch device includes: a first cam and a second cam that move in a moving direction parallel to an inclined face of a bridge cam provided on a cam plate and that engage with a butt whose protruding height from a needle bed is set to a full height and a half height by a press of a presser provided on a carriage to advance and retreat a knitting needle, the first cam having a first stitch-size determining cam face engageable with the butt of the full height to form a large-sized stitch, the second cam having a second stitch-size determining cam face engageable with the butt of the half height to form a small-sized stitch, the small-sized stitch and the large-sized stitch being formed in the same knitting course by forming a step difference between the first stitch-size determining cam face and the second stitch-size determining cam face; characterised in that it comprises a control cam that moves the first cam and the second cam in the moving direction so that the first stitch-size determining cam face and the second stitch-size determining cam face are switched between an even state and a stepped state; and drive means that drives the control cam in a rotating direction, wherein the control cam includes a first cam sliding face that moves the first cam in the moving direction by sliding contact therewith via a first sliding contact member, and a second cam sliding face that moves the second cam in the moving direction by sliding contact therewith via a second sliding contact member, and wherein a distance between the first cam sliding face and the second cam sliding face in the rotating direction of the control cam differs in a plurality of steps or in a stepless manner in a circumferential direction. a first cam and a second cam that move in a moving direction parallel to an inclined face of a bridge cam provided on a cam plate and that engage with a butt whose protruding height from a needle bed is set to a full height and a half height by a press of a presser provided on a carriage to advance and retreat a knitting needle, the first cam having a first stitch-size determining cam face engageable with the butt of the full height to form a large-sized stitch, the second cam having a second stitch-size determining cam face engageable with the butt of the half height to form a small-sized stitch, the small-sized stitch and the large-sized stitch being formed in the same knitting course by forming a step difference between the first stitch-size determining cam face and the second stitch-size determining cam face; characterised in that it comprises a control cam that moves the first cam and the second cam in the moving direction so that the first stitch-size determining cam face and the second stitch-size determining cam face are switched between an even state and a stepped state; and drive means that drives the control cam in a rotating direction, wherein the control cam includes a first cam sliding face that moves the first cam in the moving direction by sliding contact therewith via a first sliding contact member, and a second cam sliding face that moves the second cam in the moving direction by sliding contact therewith via a second sliding contact member, and wherein a distance between the first cam sliding face and the second cam sliding face in the rotating direction of the control cam differs in a plurality of steps or in a stepless manner in a circumferential direction.