To obtain a freshness-retaining agent in which allyl isothiocyanate which is a main ingredient of Japanese horseradish is used.

In the freshness-retaining agent, the allyl isothiocyanate is prepared as ≥55% aqueous solution of an alcohol thereof and pH of the aqueous solution is kept to ≤4.5. The aqueous alcohol, solution of the allyl isothiocyanate diluted in an adequate concentration does not cause precipitation and is safe because of diluted solution and enables long-time storage.