PURPOSE: To prevent an ink-supplying pressure from varying and enable an ink cartridge to be disposed at an arbitrary position in a printer, by providing a float-type valve at an ink-supplying port of an ink tank.

CONSTITUTION: When the ink level in an ink tank 5 is lowered with the progress of printing by an ink jet head 3, a float-type valve 6 is lowered to open an ink-supplying port 10, whereby an ink is supplied from an ink cartridge 13. When the ink level reaches a predetermined level, the port 10 is closed by the valve 6. Thus, the ink level in the tank 5 is constantly fixed under control, and stable jetting from the ink jet head can be ensured. Even when the pressure of the ink supplied through a supply pipe 4 is varied due to flexing motions of the pipe 4, the valve 6 functions as a damper to prevent the pressure variations from exerting undesired effects on the ink jet head 3.