PURPOSE: To automatically return ink in an atomizer to an ink can when exchanging the ink can by controlling the rotation of a screw pump in relation to the actions of each supporter for the ink atomizer and the ink can.

CONSTITUTION: A supporter 20 for an ink atomizer 30 and a supporter 60 for an ink can 61 are vertically moved in such a way as to allow them to come near each other or to separate from each other, and the supporter 60 is moved with a larger dimension than the diameter of the can 61 only toward the axial direction of a mixing roller 11 by means of an air cylinder device 62. When a valve 44 is opened by each device 30 and a printer 10 is operated, pressure wind is jetted from a pipe 37 from a nozzle 36 and divided air to a pipe 38 is jetted through a valve 39 from a nozzle 40 to turn an impeller 34. Whereupon, ink in the can 61 is drawn up by rotation of a screw shaft 33 provided integrally with the impeller and discharged near the nozzle 36 through a conduit 45. The ink is then atomized by air pressure from the nozzle 36 and supplied to the peripheral side of the roller 11. When ink in the can 61 is used up, ink is returned into the can 61 by reverse rotation of the screw pump 32 and the pump 32 is stopped.