Many antipodal distinctions may be described between paddy field and upland field which are two of the principal forms of cultivated land in Japanese agriculture. In comparison with paddy field, upland field is the form of cultivated land which is utilized for growing crops other than rice without the flooding use of water. It usually meant that upland farming was less profitable than rice farming on paddy field. As the result, every effort had been spent through generations in Japan to turn farm land into paddy field with irrigation facilities. However, the social and technological progress has increased in the possibility of artificial irrigation in upland field, and as a matter of fact, irrigated farming has been developed gradually in Japan, especially since the Second World War. Farming in upland farming areas became more intensive by irrigation. But the increase in intensity was usually brought about with the changes in the kind of crops, i. e., from less intensive to more intensive one, and also with the increase in the intensity level of multiple cropping, so that the effects of irrigation on upland farming was not so simple to be determined. If a new crop has been introduced to farm organization or if its intensity level has been shifted as the result of water use, it would necessarily bring about a great influence on the types of farming as well as the size of farm business. The authors intended to study the effects of irrigation upon changes in both the intensity and the type of farm organization in upland farming. Ayagawa Irrigation District, Miyazaki Prefecture, was the area from where the present data were acquired. Four types of farms including 22 farms all together with various vegetables in the open field were selected and enumerated for this study. They were (1) medium-sized farms with ordinary vegetables in the open field (4 farms), (2) large-sized farms with vegetables in the open field (7 farms), (3) farms with vegetables grown in both the open field and the vinylhouse (6 farms), and (4) farms with vegetables in the open field and tobacco (5 farms). The results of the present study may be summarized as follows. 1. A remarkable change had been occurred in the traditional structure of upland farming particularly during the period of years of the 1960’s. One of the most significant changes observed in upland farming areas in southern Kyushu was the transfer of crops from ordinary crops such as sweet potato, wheat and barley, rape-seeds, soybean and azuki-bean to vegetables of various kinds, forage crops and industrial crops. The factors which affected the changes seemed to be attributable to (1) changes in consumption and demand of foods, (2) international trade and price level in domestic market, (3) technological development including the development in farm mechanization, in technique of growing crops in vinylhouse, chemical control of pests and disease, and so forth. The changes of upland farming was much more striking in the irrigation areas. 2. The ratio of water use has been gradually increased in Ayagawa Irrigation District. At that time, the main purposes of water use were (1) crop protection from drought, (2) preparation of seed-bed, (3) crop protection from pests and disease, (4) dust-cleaning, (5) washing products before shipping and (6) cooling of cowshed. A great diversity in the purposes was one of the characteristic features of water use in the case of irrigated areas in southern Kyushu. 3. The ratio of water use was relatively high on farms with vegetables in the open field, especially on medium-sized one. In spite of high intensity of water use as well as land use on medium-sized farms, the amount of farm earnings was the smallest on this group of farms probably due to small size in the total volume of farm business. 4. Large-sized farms with vegetables in the open field seemed to have a larger possibility in adopting crop rotation system on irrigated upland field. However, reasonable crop rotation system has not been established yet on this type of farms. 5. Farms with both types of vegetables grown in the open field and vinylhouse were more intensive than farms with vegetables only in the open field. The amount of farm earnings was remarkably larger, but the ratio of land use was low. It was because that the vinylhouse were usually fixed for many years on the particular field and most of the family labor had to be put into crops in the vinylhouse. The conflicts as for land utilization seemed to be severe on this type of farms. 6. Farms with vegetables in the open field and tobacco also had conflicts to a considerable extent as for land use, since tobacco was the main crop on this type of farms. Vegetables in the open field had been grown less intensively and the ratio of water use relatively low. on farms belonging to this type. 7. Water use on upland field affected to increase in the acreage of vegetables in the open field and in the degree of intensity of land use, but tended at the same time to accelerate the diversification of crops and differentiation of types of farming in the case of Ayagawa Irrigation District. Larger-sized farms with various kinds of vegetables grown in the open field seemed to be the type of farms which ought to be encouraged in increase in number from the viewpoint of land and water use. Then, new crop rotation systems which will utilize water resource more effectively and irrigation system including flooding use of water seems desirable to be developed for the future development of upland farming.