An object of the present invention is to increase the rate at which lignan-class compounds are absorbed into the body, namely, to provide fast-acting lignan-class compounds.Provided is an oil-in-water emulsion which comprises a water phase and an oil phase comprising at least one kind of lignan-class compounds dissolved therein and being emulsified in the water phase, wherein the oil droplets which serve as a dispersion phase in the emulsion are made finer by high-speed agitation or other method so that their average particle size is 1000 nm or smaller, preferably 500 nm or smaller, and more preferably 300 nm or smaller, whereby the rate at which lignan-class compounds are absorbed into the body is improved to impart immediate action.