Tooth whitening agent

Provided is a tooth-whitening agent which exhibits immediate tooth-brightening and -whitening effects. A tooth-whitening agent which is provided with a composition (A) and a composition (B) in a separate state and which is to be used by applying the compositions (A) and (B) alternately to a tooth, wherein: the composition (A) is a composition which contains 0.1 to 30 mass% of phytic acid or a salt thereof in terms of the acid, which does not contain any polyvalent metal cation, or alternatively contains such cations in a molar amount of less than 0.1 time that of phytic acid or the salt thereof, which exhibits a pH of 4 to 6.5 at 25oC, and which contains a fluoride compound in an amount such that the ratio of the mass of the fluoride compound in terms of fluorine atoms to the mass of phytic acid in terms of the acid [(the amount in terms of fluorine atoms)/phytic acid] is 0.05 or less, or alternatively does not contain any fluoride compound; and the composition (B) is a composition which contains one or more selected from among orthophosphoric acid, condensed phosphoric acids and salts thereof in an amount of 0.01 to 15 mass% in terms of the acid and which exhibits a pH of more than 6.5 to 10.5 at 25DEG C.