An ink liquid supply system for an ink jet system printer comprising an ink liquid reservoir for containing ink liquid therein, and a constant flow rate pump for supplying the ink liquid to a nozzle. The constant flow rate pump integrally includes three pressure chambers, which are divided by two diaphragms and coaxial pistons. The first pressure chamber functions to introduce an ink liquid collected by a beam gutter of the ink jet system printer for returning the ink liquid to the ink liquid reservoir. The second pressure chamber functions to introduce the ink liquid from the ink liquid reservoir and develop the ink liquid toward the third pressure chamber. The third pressure chamber receives the ink liquid from the second pressure chamber and develops the ink liquid to the nozzle.