A purification method according to the present invention is for either a compound expressed by a formula (1) or a resin having the structure exhibited by a formula (2), and contains a step in which an acidic water-soluble solution is contacted with a solution (A) containing either the compound or the resin and an organic solvent optionally not mixed with water. In the formula, X is an oxygen atom or a sulphur atom, R1 is a single bond or a hydrocarbon group, R2 is an alkyl group or a hydroxyl group, etc., and at least one of R2 is a hydroxyl group, R3 is a single bond or an alkylene group, m is 1-6, m2 is 1-5, p is 0 or 1, and n is 1-4.