The object is to improve shock resistance of a double tube allyl isothiocyanate volatile agent comprising a breakable inner vessel sealing allyl isothiocyanate therein and a flexible outer vessel made of allyl isothiocyanate-permeable resin sealing the inner vessel therein so as to prevent unintended breakage of the inner vessel and consequent start of volatilization. The ratio Y/X of the inner length X of the outer vessel and the outer length Y of the inner vessel is determined to be 94% or over and 99.9% or under, and ratio Q/P of the inner diameter P of the outer vessel and the outer diameter Q of the inner vessel is determined to be 75% or over and 99.9% or under.
