Coastal dune vegetation is currently under threat of extinction in many places. In that context, this study implemented two investigations along the Genkai Sea coast of the Itoshima Peninsula, Fukuoka Prefecture, Japan First, a survey of plant species composition was done at three beaches (Nagahama, Keya and Niginohama), in order to (1) valuate the state of coastal vegetation under different beach development conditions, and (2) identify how human impacts such as beach development affect plant species in coastal dunes. The survey results revealed (1) similar plant species at Nagahama and Niginohama, where the beach development rate has been relatively low, in contrast to (2) different plant composition at Keya, specifically more terrestrial plants where the development rate has been high. Second, the spatial distribution of ten representative beach plants was investigated at Nagahama in October 2018. The survey found that (a) Carex kobomugi Ohwi and Artemisia capillaris were distributed throughout the dunes, (b) Melanthera prostrata and Ixeris repens had high distribution along the shore, and (c) Sedum japonicum Siebold had high diversity near the pine forest. These results suggest that human disturbances and developments such as parking lot and beach house construction have reduced the habitat for plant species on the seaside. The positioning of some facilities, such as a seawall set-back at Keya and protection-forest at Nagahama, have some impacts on vegetation, such as enabling the intrusion of terrestrial plants and alien species. In order to conserve coastal dune vegetation, it is necessary to seek a balance between dune habitat and the seashore environment. In addition, more consideration can be given to the location of some facilities in order to avoid destroying the habitat of the coastal dune vegetation.