In this study, a rotary equipped with devices for preventing alien substance from being wound and for preventing soil adherence were developed and their performances are evaluated in the field. The former device was effective in the paddy field with low moisture content, but power requirement of rotary tilling was increased in the field with high moisture content. In the field test of rotaries equipped with device to prevent the power requirements were measured to be 52.18, 52.44, 49.01 and 46.34 PS for general, stainless steel, rubber and PE rotaries, and the quantities of the soil adhered to rotaries, on the average, were to be 5.6, 5.7, 3.1 and 2.7 kg for general, stainless steel, rubber and PE rotaries, respectively. The PE rotary cover reduced the power requirement and soil adherence by 11 and 52%, respectively.