PROBLEM TO BE SOLVED: To provide the wood preservative for safe incineration. SOLUTION: The wood preservative agent contains compound A1 which is the salt of a positive ion represented by the formula [R1, R2 are each independently an 8-18C straight chain alkyl, R3 is oxyethyl represented by (CH2CH2O)n (n is 1 or 2) or methyl and R4 is methyl] and a counterion containing no halogen atoms and compound B which is at least one compound selected from the group of the disinfectants of phenol, furancarboxylic acid, copper and zink and contains no halogen atoms.