Patent ID: 8167417

Claim:
A discharge unit, comprising: an ink tank in which an ink for discharging to an object to be treated is placed; and a pressure control device connected to the ink tank, wherein the pressure control device has: first and second flow paths being provided between the ink tank and an outside atmosphere; a negative pressure valve, provided in the first flow path, the negative pressure valve being configured to allow the ink tank to connect to the outside atmosphere when the internal pressure of the ink tank is smaller than the pressure of the outside atmosphere by a first predetermined pressure or more, and configured to shield the ink tank from the outside atmosphere when the internal pressure of the ink tank is not smaller than the pressure of the outside atmosphere by the first predetermined pressure or more; and a positive pressure valve, provided in the second flow path, the positive pressure valve being configured to allow the ink tank to connect to the outside atmosphere when the internal pressure of the ink tank is larger than the pressure of the outside atmosphere by a second predetermined pressure or more, and configured to shield the ink tank from the outside atmosphere when the internal pressure of the ink tank is not larger than the pressure of the outside atmosphere by a second predetermined pressure or more; wherein a backing pressure inside the ink tank is controlled without using a porous body.