The Japanese vetch (Vicia japonica) belongs to Fabaceae (the Pea family). It is a perennial herb that is distributed northward from Kinki district of Honshu to Hokkaido, the Kuril Islands, Sakhalin and the Korean Peninsula. This herb grows in coastal grasslands, and can reach about 1 m long. The leaves are pari-pinnate compound with 10-16 elliptic leaflets. The rear surface of leaflet is covered with soft hairs. The short racemes are borne on the axils, and the pale magenta, papilionacenous flowers bloom from June to September.