The present invention provides a novel mycovirus that suppresses phytopathogenic fungi and a novel method for controlling plant diseases. A novel mycovirus that is present endogenously in a predetermined rice blast fungus, has four types of double-stranded RNAs of 2.8 to 3.6 kb, and suppresses a phytopathogenic fungus has been found. This virus suppresses phytopathogenic fungi such as rice blast fungus.