The present invention relates to a method for enhancing a plant’s resistance to fungal diseases by reducing expression of polyphenol oxidase. A trim cover is provided, sewn along the entire periphery at the mutual contact position of an upper and lower cover, the pulled-in state is modulated by cloth pieces, thereby preventing wrinkles. At least one of the first and second piezoelectric elements is contracted and expanded in a direction substantially parallel to a surface of the disk, in the presence of an applied voltage so that the slider provided on the third portion is.