This paper presents a new method of numerical analysis of 2-dimensionnl incompressible flow which is useful for a stage of product design, developed on the basis of both FEM and FDM, and also a new model of vorticity shedding has been developed. A computer simulation program was employed to confirm the following features of the present method. 1) The flexibility of any object shape by FEM. 2) The stability of the calculation by the modified FLIC* method (FDM). 3) The approximation of the flow separation on the boundary by the vorticity generating model. After applying the program to the design of the two types of air flow meters; i.e., the vane and Karman types, it has been found that the program is practically useful to obtain the optimum design of air flow meters.