Abstract: An ink jet printing device for manufacturing an organic electroluminescent device. The ink jet printing device includes a chamber, an inkjet unit, and a pressure adjusting unit. The chamber has a space, and a basement is provided inside the space for supporting the organic electroluminescent device. The inkjet unit has a print head, which includes print holes. The print head is set in the chamber and is used to inject ink toward a substrate of the organic electroluminescent device. The pressure adjusting unit connects to the space so as to steady the pressure of the space within a specific value. Furthermore, an ink jet printing method for manufacturing an organic electroluminescent device is also disclosed.