PURPOSE: To obtain a therapeutic agent containing allomatol which is a kojic acid derivative as an active ingredient and useful for endogenous chloasma, senile lentigo, solar lentigo and post-inflammatory pigmental spot which are regarded as intractables.

CONSTITUTION: A drug, containing allomatol (a kojic acid derivative) expressed by the formula as an active ingredient and capable of effectively treating senile and solar lentigo, post-inflammatory pigmental spot, etc., endogenous chloasma, etc., occurring without originating from the irritation by the external world. The allomatol is obtained by converting hydroxymethyl group of the kojic acid into chloromethyl group, then converting the resultant group into methyl group by reductive reaction. Since the aforementioned drug can be applied to affected parts mainly by percutaneous administration, the drug is prepared in the form of ointments, solutions, lotions, creams, aerosols, cataplasmas, plasters, etc. The above-mentioned drug is safe and extremely effectively cures the pigmentation without any side effects.