A mixing device for a cell printing composition, the mixing device comprising: a first syringe comprising a first container for containing first liquid, a first moving element discharging the first liquid contained in the first container; a second syringe comprising a second container for containing second liquid, a second moving element discharging the second liquid contained in the second container; a mixing container comprising a rotating mixing unit, where the discharged first liquid and the discharged second liquids enter and are mixed each other; a power transmission unit for driving the first moving element, the second moving element and the mixing unit; a first threaded guide where the first moving element is movably connected; a second threaded guide where the second moving element is movably connected; and a rod for rotating the mixing unit; wherein the first moving element is movable by the rotation of the first threaded guide; the second moving element is movable by the rotation of the second threaded guide; and the first threaded guide, the second threaded guide, and the rod are rotatable by the power transmission unit, characterized in that the power transmission unit comprises a ring gear, a sun gear which is rotatable by the rotation of the ring gear, a first planetary gear which engages with the sun gear, and a second planetary gear which engages with the sun gear; and wherein the first threaded guide is rotatable by the first planetary gear; the second threaded guide is rotatable by the second planetary gear; and the rod is rotatable by the sun gear, wherein the first moving element is connected to the first threaded guide via a first connecting portion which is guidable by the first threaded guide; and the second moving element is connected to the second threaded guide via a second connecting portion which is guidable by the second threaded guide, wherein the mixing device further comprises a first guard portion having a first slot where the first connecting portion is guidable; and a second guard portion having a second slot where the second connecting portion is guidable. a first syringe comprising a first container for containing first liquid, a first moving element discharging the first liquid contained in the first container; a second syringe comprising a second container for containing second liquid, a second moving element discharging the second liquid contained in the second container; a mixing container comprising a rotating mixing unit, where the discharged first liquid and the discharged second liquids enter and are mixed each other; a power transmission unit for driving the first moving element, the second moving element and the mixing unit; a first threaded guide where the first moving element is movably connected; a second threaded guide where the second moving element is movably connected; and a rod for rotating the mixing unit; wherein the first moving element is movable by the rotation of the first threaded guide; the second moving element is movable by the rotation of the second threaded guide; and the first threaded guide, the second threaded guide, and the rod are rotatable by the power transmission unit, characterized in that the power transmission unit comprises a ring gear, a sun gear which is rotatable by the rotation of the ring gear, a first planetary gear which engages with the sun gear, and a second planetary gear which engages with the sun gear; and wherein the first threaded guide is rotatable by the first planetary gear; the second threaded guide is rotatable by the second planetary gear; and the rod is rotatable by the sun gear, wherein the first moving element is connected to the first threaded guide via a first connecting portion which is guidable by the first threaded guide; and the second moving element is connected to the second threaded guide via a second connecting portion which is guidable by the second threaded guide, wherein the mixing device further comprises a first guard portion having a first slot where the first connecting portion is guidable; and a second guard portion having a second slot where the second connecting portion is guidable.