PURPOSE: To enable a printing ink to be ejectingly supplied into an ink fountain by measuring the ink level in the ink fountain by a sensor, and externally pressing a printing ink bag automatically when the ink level is not more then a set value.

CONSTITUTION: A printing ink bag A is formed from a fabric (a) in which an inner layer 1 and an outer layer 2 made of a flexible synthetic resin film and treated for screening of UV rays are stuck to each other by an adhesive 3 containing a UV-screening agent, based on benzophenol or the like. The bag A is funnel-shaped on one side of its body part, and is provided with an ejecting pipe 4 at the tip of the funnel-shaped part. When a power supply for a controller 28 is switched ON, the ink level in an ink fountain 9 is first measured by an ink level sensor 13. When the ink level is not more than a set value, a clamping frame 25 is lowered by operating a solenoid 23, thereby relieving a feeding pipe 27 from a blocked condition, and the bag A is forcibly raised to between clamping rollers 14, 14'. The bag A is thereby pressed, and an ink in a desired amount corresponding to the rise is supplied into an ink fountain 9.