A radio wave lens antenna device including a semispherical Luneburg lens and a radio wave reflection plate. The radio wave lens antenna device prevents the signal reception sensitivity from being lowered in rain or snow. The radio wave lens antenna device includes a semispherical Luneburg lens 1, a radio wave reflection plate 2 that is larger than the diameter of the lens, an antenna element 3, and a holder 4 that holds the antenna element. The radio wave reflection plate 2 is arranged in an erected state. An ice-snow-water resistant means, which includes a first cover 5 and a second cover 6, prevents rain, snow, and ice from collecting and running off the Luneburg lens.