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This paper proposes a reflectarray antenna consisting of arbitrarily-shaped conductor elements on a flat surface. Reflectarray antennas with specified elements have been developed as a high-gain antenna and they can be applied to design for millimeter-wave antennas [1], deployable antennas [2] and millimeter wave imaging system [3]. Reflectarray antenna transforms an incident spherical wave into a planar one by adjusting the reflection-phase property on the aperture. The reflection phase of each element greatly depends on the frequency. Therefore, as long as the elements with similar phase characteristic are not used, a phase error due to difference between the frequency characteristics cause a gain loss and an increase of side-lobe level. So, it is firstly important that we find a group of resonance elements with similar frequency characteristics and arbitrary phase value in the range from 0 to 360 degrees. However, when the arbitrary shaped elements that we have developed [4] are used for antenna design, the mutual coupling between the adjacent elements often causes the unexpected phase properties, so that the antenna performance is deteriorated. So, in this paper, we propose arbitrarily-shaped elements suppressing such a mutual coupling. An example of a reflectarray antenna designed by using them is demonstrated, and the measurement of the fabricated reflectarray antenna verifies its usefulness. [ABSTRACT FROM PUBLISHER]