The purpose of this paper is to analyze the account books of the Dutch factory at Deshima in Japan which cover the period from 1641 to 1805, and to clarify how to calculate the actual figures of the Japanese-Dutch trade. It is well known that the Dutch East India Company(Vercenigde Nederlandsche Oost Indische Compagnie) conducted trade with Japan during the 17th and 18th centuries. In 1609, the company established a factory at Hirado which, in 1641, was ordered to move to Deshima. In both factories the Dutch merchants kept their account books according to the Italian system of book-keeping. These books recorded the quality, quantity and price of the goods imported, exported and negotiated with the Japanese merchants. At present, thse account books-for example, the ledgers(Negotie Grootboeken) and journals(Negotie Journaalen)-are preserved in the Netherlands Public Record Office(Algemeen Rijksarchief) in the Hague. In the past, Oskar NACHOD and other scholars in Japan have made use of these archival materials for their analysis of the management of the Dutch factory in Japan. However, because they did not understand the bookkeeping system of the Dutch factory, the results of their circulations concerning the volume of the trade between Japan and the Dutch East India Company are not precise. This paper tries to clarify the bookkeeping and accounting system used at Deshima, taking the records of the year 1642 to present a case study of the system of double entry bookkeeping, branch accounting, i.e. the relationships between the main office at Batavia and the branch offices of Deshima, Taiwan and Tonkin, the "closing" of the books etc., and intends to correct the results of the calculations by O. NACHOD and other scholars. The above mentioned commercial records give a detailed picture of the yearly trade between Japan and the Dutch East India Company, but we can nort understand the exact volume recorded in them, unless we have a clear idea of the way in which they were organized.