To simplify the structure of components, to improve the durability of a moving part and to facilitate the operation by turning an arm ring on the surface of a support cylinder so as to attain expansion and folding of antenna elements.

Arm rings 12A-12H turned around a support pole 11 are stacked and, arranged at a tip of the support pole 11 in a direction of the support shaft. A support arm 13W1 or the like extended in a direction orthogonal to the support shaft is fixed to each of the arm rings 12A-12H. Antenna elements 14A1, 14A2 or the like are fixed to the ends of the arm rings 12A-12H. Then marking is applied to the surface of the arm rings 12A-12H and positioning is made, then in the case of expanding the antenna 10, antenna elements 14A1-14H2 are easily spread radially at an equal interval. In the case of folding the antenna 10, a push screw 15 is loosened to set the turning of the arm rings 12A-12H free thereby collecting other support arms to the center.