The present invention provides a whitening agent that can be acquired from naturai source, has high safety when administered to the human beings, can ensure a stable supply, and has satisfactory patient compliance, characterized in comprising the solvent extract of a plant which is Quercus species of the Fagaceae family.本發明提供來源於自然、對人體之安全性高、無供應穩定性問題且服藥順從性能令人滿意之美白劑,其特徵為含有山毛櫸類等殼斗科檞屬植物之溶劑萃取物。