Diadema setosum is one of the warm water species of sea urchins forming urchinbarren in southern Japan. D. setosum is seldom eaten because of its peculiar bitterness of the gonads. However, in Kagoshima and Kumamoto Prefectures in Kyushu, southern Japan, D. setosum is caught by the local diving fishermen and the gonads are eaten as sashimi by the local people. The object of this paper is to explain why the supply and demand of D. setosum goes on in the prefectures. The investigation has revealed the mechanism of keeping the supply and demand as follows. Aspect of supply, there is only a fishery for D. setosum from December to March, which diving fishermen can earn modest gains. Aspect of distribution, processor-cum-wholesalers fulfill a role to connect fisheries with markets. Aspect of consumption, product of D. setosum has good things which are cheaper and longer expiration date than other sea urchins and made in Japan. Furthermore, the defect for the taste of D. setosum is filled the gap by peculiar soy source which is sweet and thick and is been fond by people in Kyusyu.
