Root endophyte which live symbiotically within a root of crops were separated and classified. A medium which cultured the strains were inoculated with a seed of a crop. The seed was allowed to sprout to inoculate the root of the crop with root endophytes. While growing the crop, the soil for growth was inoculated with soil pathogenic bacteria, and the crop was grown for a period necessary for the occurrence of a soil disease. The crop was inspected for pathopoiesis, and root endophytes, which had been inoculated into the root of crop having low severity, were specified and selected. As a result, it was found that some root endophytes can significantly inhibit soil diseases. Among root endophytes, Heteroconium chaetospira was found to be particularly effective in inhibiting soil diseases.