Disclosed is a preservative for preserving wood comprising 5-methyl-2-trifluoromethylfuran-3-carboxylic acid anilide derivative represented by formula (A), wherein R represents an isopropyl group or an isopropoxy group, as an active ingredient. The preservative for preserving wood has an excellent preservative effect on various wood-decay fungi at an extremely low dose, is economically efficient, and imposes a small burden on the environment. Also disclosed is a method for treating wood using the preservative.