The present disclosure relates to a method of increasing an amount of a stilbenoid, and/or one or more compounds selected from the group consisting of TCA cycle metabolites, polyamine alkaloids, 4-aminobutyric acid, abscisic acid and salts thereof in a plant, the method comprising steps of: irradiating the plant, part, crushed material or cultured plant cell with light, wherein a fluence at a wavelength range of 275-295 nm is 50,000-2,500,000 μmol/m2, while at the same time a fluence at a wavelength range of 200-270 nm is less than 20% of the fluence at the wavelength range of 275-295 nm; and storing the irradiated plant, part, crushed material or cultured plant cell in a dark place for 1 day or more.