A device for forming a round bar into variable shapes where a diameter of a passage hole varies, the device comprising: a main body provided with a plate portion with a circular shape having a plate hole formed in a center thereof, having four or more of plate protrusions protruding to the plate portion in a radial shape, and a turn gear connecting portion formed at an outer circumference surface of the plate portion; a round bar forming portion coupled between the four or more of plate protrusions and having four or more slide molds seated on the plate portion and four or more forming rolls coupled to the slide molds to rotate respectively; and a turn gear having a donut shape where two main gears are connected to an outer surface thereof, provided with four or more turn gear protruding portions with a curved arc shape having different distances from a center in an inner surface thereof, and disposed between the slide mold and the turn gear connecting portion, a main body cover connected to a front portion of the main body and provided with two deceleration motor connecting portions in a front side thereof; and a deceleration motor coupled to the deceleration motor connecting portions and having a pinion gear which is rotatably interlocked with the main gears at a driving axis; characterized in that a step is formed in the round bar forming portion, and the round bar forming portion with the step and the round bar forming portion without the step are alternately disposed; and wherein a distance between a center of the plate hole and the slide mold at a side where the step is formed is larger or smaller than a distance between a center of the plate hole and the slide mold at a side where the step is not formed. a main body provided with a plate portion with a circular shape having a plate hole formed in a center thereof, having four or more of plate protrusions protruding to the plate portion in a radial shape, and a turn gear connecting portion formed at an outer circumference surface of the plate portion; a round bar forming portion coupled between the four or more of plate protrusions and having four or more slide molds seated on the plate portion and four or more forming rolls coupled to the slide molds to rotate respectively; and a turn gear having a donut shape where two main gears are connected to an outer surface thereof, provided with four or more turn gear protruding portions with a curved arc shape having different distances from a center in an inner surface thereof, and disposed between the slide mold and the turn gear connecting portion, a main body cover connected to a front portion of the main body and provided with two deceleration motor connecting portions in a front side thereof; and a deceleration motor coupled to the deceleration motor connecting portions and having a pinion gear which is rotatably interlocked with the main gears at a driving axis; characterized in that a step is formed in the round bar forming portion, and the round bar forming portion with the step and the round bar forming portion without the step are alternately disposed; and wherein a distance between a center of the plate hole and the slide mold at a side where the step is formed is larger or smaller than a distance between a center of the plate hole and the slide mold at a side where the step is not formed.