One of the biggest changes of agriculture in Japan after the war, has been the mechanization of farm operations. Several kinds of small tillers, worked by kerosene engine, have gradually become popular implements of our farms. Therefore, the present writer wants to analize the changes of labor management that appears to be influenced by the mechanization. But it was difficult to take out the pure effects of machines out of the actual farm managements, for they are the farthest from being able to be treated in the laboratory experiment. When we come to survey the actual farm managements, we often come across the phenomena in which the effects of many factors are intertwined. We can not differenciate them clearly. Then, we asked the Okayama Statistical Office of Agriculture and Forestry Department to allow us to use the basic data for the survey of rice production cost. Even though the data are not always suitable for our purpose, they seem to be the best that are available. Rearranging this basic data for our purpose, we could classify the surveyed farms into three groups which are selected throughout the Okayama Prefecture. According to this classification, there are three types of farm groups; the first (A, A1 and A2) is the large scale farms which are possesed of a small tiller, the second (B, B1 and B2) is the small scale farms which are not possesed of a small tiller but hire it; and the third (C, C1 and C2) is the small or medium scale farms which neither are possesed of nor hire a small tiller. Analyzing the differences among these farm groups, we can find the following trends. (See table 1-7) 1) Speaking on the differences of farm scale among three groups, A groups (A, A1 and A2) are larger than any other groups. 2) Speaking on the differences of commercial crops production among three groups, A groups are most devoted to them and the farms of B groups (B, B1 and B2) are usually the part-time ones. 3) As far as total. working hour for rice production per unit area is concerned, A groups are the least one of these three groups but the differences of working hour among them are relatively slight. 4) The working hour of woman as a family member is shorter in A groups than in other groups. The working hour of hired men, however, is longer in A groups than in other groups. It seems to express that the changes of operater's role in family farm have been affected by mechanization. 5) It is certain that the farms of A groups have the convenient machines and save their labor, but only a few kinds of operations for rice production are practiced by mechanical method and most parts of this operations are practiced by hand method. Therefore, even the farmers of A groups still have to do many hand work for his farm management and sometimes they devote intensive hand practice to their rice production.