The purpose of this study is to elucidate a structure of internal flow in air-driven ejector. The air-driven ejector is used as a part of automatic conveyance systems, in which precision components and food are handled utilizing vacuum pressure produced by the ejector. So far, the air-driven ejector has been designed mostly by experience because the internal flow in air-driven ejector is not well analyzed. The flow field of ejector is so small that conventional measurements cannot be employed and it is difficult to obtain the detailed information. Thus, internal flow in the air-driven ejector is simulated on water table using hydraulic analogy. In this paper, we examined the influence of the different radius of curvature of the nozzle on the flow field. It is found that in the case of the large radius of curvature, jet from the nozzle didn't become wider than small radius of curvature. And lowest pressure in the vacuum room is obtained at higher than nozzle pressure ratio 6.0.