A 3D printer having a cooling function, the 3D printer comprising: a tank configured to store therein a photocurable liquid resin; a bed configured to be moveable in a vertical direction within the tank and to support a shaping object; a bed transfer unit configured to move the bed in the vertical direction; a light projection unit configured to linearly project laser light to the photocurable liquid resin stored in the tank in a longitudinal direction of the tank so as to cure the photocurable liquid resin into the shaping object; a light projection unit transfer unit configured to move the light projection unit in a width direction of the tank; a control unit configured to control operations of the light projection unit, the light projection unit transfer unit, and the bed transfer unit; and a cooling unit installed on one side of the light projection unit and configured to dissipate heat generated from the light projection unit, the light projection unit comprising: a light projection unit main body fixed to the light projection unit transfer unit so as to be transferred in the width direction of the tank; a laser diode embedded in the light projection unit main body and configured to project laser light in one direction; a polygon mirror embedded in the light projection unit main body and configured to linearly reflect the laser light projected from the laser diode in the longitudinal direction of the tank while rotating; and a refraction mirror installed within the light projection unit main body and configured to refract the laser light reflected from the polygon mirror to the photocurable liquid resin within the tank, the polygon mirror comprising a rotation shaft disposed perpendicular to a surface of the liquid resin within the tank so as to have a rotation plane parallel to the surface of the liquid resin. a tank configured to store therein a photocurable liquid resin; a bed configured to be moveable in a vertical direction within the tank and to support a shaping object; a bed transfer unit configured to move the bed in the vertical direction; a light projection unit configured to linearly project laser light to the photocurable liquid resin stored in the tank in a longitudinal direction of the tank so as to cure the photocurable liquid resin into the shaping object; a light projection unit transfer unit configured to move the light projection unit in a width direction of the tank; a control unit configured to control operations of the light projection unit, the light projection unit transfer unit, and the bed transfer unit; and a cooling unit installed on one side of the light projection unit and configured to dissipate heat generated from the light projection unit, the light projection unit comprising: a light projection unit main body fixed to the light projection unit transfer unit so as to be transferred in the width direction of the tank; a laser diode embedded in the light projection unit main body and configured to project laser light in one direction; a polygon mirror embedded in the light projection unit main body and configured to linearly reflect the laser light projected from the laser diode in the longitudinal direction of the tank while rotating; and a refraction mirror installed within the light projection unit main body and configured to refract the laser light reflected from the polygon mirror to the photocurable liquid resin within the tank, the polygon mirror comprising a rotation shaft disposed perpendicular to a surface of the liquid resin within the tank so as to have a rotation plane parallel to the surface of the liquid resin. a light projection unit main body fixed to the light projection unit transfer unit so as to be transferred in the width direction of the tank; a laser diode embedded in the light projection unit main body and configured to project laser light in one direction; a polygon mirror embedded in the light projection unit main body and configured to linearly reflect the laser light projected from the laser diode in the longitudinal direction of the tank while rotating; and a refraction mirror installed within the light projection unit main body and configured to refract the laser light reflected from the polygon mirror to the photocurable liquid resin within the tank, the polygon mirror comprising a rotation shaft disposed perpendicular to a surface of the liquid resin within the tank so as to have a rotation plane parallel to the surface of the liquid resin.