To provide an alkyl ammonium salt type wood antiseptic in which the corrosion of iron materials is restrained.

A wood antiseptic containing an alkyl ammonium salt as a main agent is incorporated with one or more kinds of heterocyclic alkyl ammonium salts selected from the group consisting of alkyl pyridinium salts, alkyl quinolinium salts, and alkyl isoquinolinium salts. Preferably, the heterocyclic alkyl ammonium salt has 8-18C alkyl group and the alkyl ammonium salt as the main agent is didecyl dimethyl ammonium chloride.