This study was canied out to ddermine optimum areas for various sizes of land coverage of the farm machinery utilization in 1993-1994. A kind of machinery size and work systems were classed as the power tiller of 10HP+man power, the tractor of 35~46HP (tractor of 64~86HP and attachment were leased to harvest work), 64-86HP+ attachment and 90- 105HP+ attachment, respectively. ulcornerhe results are summarized as follows: 1. The optimum areas of tractors of 90~105HP, 64~86HP and the power tiller of lOHP were estimated as 21.9 (corn-rye cropping system)- 26.9ha (sorghum $ imes$ sudangrass - rye cropping system), 14.7 - 22.8ha and 1.2 - 1.61ha, respectively. The break-even-point areas of the tractors of 90-105HP. 64-86HP and the power tiller of lOHP were 16.6 (corn-rye cropping system)- 19.9ha (sorghum $ imes$ sudangrass - rye cropping system), 12.5 - 16.lha and 0.12-0.13ha, respectively. 2. The optimum areas (land sizes, annual field capacity) for 50 cows by feeding rate(%) of roughage to concentrate were 6.8ha, 13.6ha in the 4060, 8.5ha, 17.0ha in the 5050 and 10.2ha, 20.4ha in the 60:40, and in case of 30 cows, it were 4.lha, 8.2ha in the 40:60, respectively. In the former case for the form of work system was the trador of 90-105HP+attachment and 64~86HP+ attachment, and the latter was the tractor of 35~46HP (tractor of 64~86HP and attachment were leased to harvest work) and 64-86HP+ attachment. 3. Productiori cost for corn-rye cropping system reducted to 51.8% in 102.9 wonkg dry matter the tractor of 90~ 105HP+ attachment with 213.4 wonkg dry matter the power tiller of 10HP+ man power.