The Japanese vegetable market is characterized by a general tendency towards the concentration of production by region. Amongst all vegetables, potato production has the highest level of concentration. Eighty-six percent of the total market quantity is accounted for by Hokkaido, the largest production prefecture amongst the 47 prefectures in Japan. The Herfindahl Index for prefectures in the Japanese potato market was 0.74 in 1994, indicating that the fewness of producers was equivalent to a market where total output was shared equally by only 1.35 producers. Under this highly concentrated situation, existence of monopolistic power, or more generally, oligopolistic power, of the large scale producers can be suspected. / In this thesis, the level of competition in the Japanese Potato market was evaluated employing conjectural variations analysis based on a monthly data for 1989 to 1995 to reveal the nature of the market. Four wholesale markets, in four large consumption areas, and eight production areas in differ ent geographical locations in were analyzed. / The conclusion from the results of the empirical analysis is that, despite the high level of concentration in production, all producing regions including the dominant producer, Hokkaido, seem to have behaved competitively. / One implication for the competitive behavior of these large producers is the imperative to maintain their share in the market against potential competitors, resulting in price setting close to the marginal cost.

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