Provided is a 3D printing apparatus. The 3D printing apparatus includes a build tray on which a building object is layered, a head unit including a plurality of nozzles for spraying a source ink having a gel state onto the build tray, a curing lamp curing the source ink sprayed onto the build tray, and a maintenance unit disposed under the head unit to clean the source ink attached to the nozzles. The maintenance unit includes a case, a nozzle cleaner accommodated in the case to clean the source ink attached to the nozzles by horizontally moving in contact with the head unit, a moving unit disposed in the case, the moving unit being connected to the nozzle cleaner to move the nozzle cleaner in a front/rear direction of the head unit. The nozzle cleaner includes a cleaner housing connected to the moving unit and a cleaning part mounted on the cleaner housing to perform a suction operation for suctioning the ink attached to the nozzles and a wiping operation for wiping the ink the attached to the nozzles.