A numerical analysis is performed with two-dimensional wave code for effective excitation of the m = + 1 fast Alfvén waves in an axisymmetric central cell of GAMMA 10. Plasma production with fast waves depends on the wave excitation in the plasma. Eigenmodes are strongly formed with large amplitude when the boundary conditions are satisfied. As an optimum density for each eigenmode exists discretely, the density is clamped at the value where the eigenmode is strongly formed. For higher density plasma production, formation of eigenmodes should be controlled as the density increases. In this study, pairs of phased antennas are adopted for the effective excitation of eigenmodes. The optimum configuration of antennas and their phase difference are investigated in the present geometry. It is found that the eigenmodes can be effectively excited by controlling the phase difference between a pair of antennas.