This paper proposes a novel dual frequency reflectarray such as the electric field of the reflectarray elements have not only the desired reflection phase but also the same amplitude among them.. In design of a reflectarray, we employ the particle swam optimization (PSO) which simultaneously achieves desired amplitude and phase shift at both frequencies of 1.0 GHz and 1.5 GHz. Two-layer structure is adopted to increase design freedom. In the two layers, the presence or not of a 4 by 4 metallic patch on mesh is determined by PSO, and moved in axial symmetry about x- and y-axes. As a result, we develop a dual frequency reflectarray with which the plane wave is radiated in direction of -30 degrees when the angle of incidence from illuminator is 0 degree.