Ink supply device, ink-jet recording device, and method of supplying ink

An ink-jet recording device comprising:

• a recording head unit including a recording head that ejects ink drops onto a recording medium on the basis of image information and a sub ink tank provided with an air communication hole;
• an ink supply unit that supplies an ink to the sub ink tank by reducing a pressure of the inside of the sub ink tank through a pressure reduction part, the ink supply unit being provided with an air suction member and an ink supply member that are connected to the sub ink tank;
• and
• a sealing part that at least implements sealing of the air communication hole while the ink supply unit is reducing the pressure inside the sub ink tank;
• wherein the sealing part, air suction member and ink supply member are in substantial vertical alignment.