With increasing focus on environmental effects and the need for fuel diversity in gas turbines, good liquid atomization is increasingly important. It is known that impinging atomization is able to produce fine drops by impingement of fast liquid jets. However, the atomization characteristics deteriorate at lower injection velocities. In this study, for improving atomization characteristics under a wide range of injection velocity, an effective technique is verified utilizing a small amount of gas (microjet) injection. The microjet is supplied from a pressurized reservoir independent of the liquid supply system, and it is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effectiveness, experimental visualizations and drop size measurements are carried out. It is found that atomization is remarkably promoted when the dynamic pressure of microjet overcomes that of the liquid at the impingement point. By the microjet injection with only 1% of liquid mass flow rate, Sauter mean diameter (SMD) becomes one-tenth of the original SMD. In addition, optimized atomization efficiency is successfully achieved when the dynamic pressure of the microjet is two times that of the liquid at the impingement point.