The present invention addresses the problem of providing a superior prophylactic or therapeutic agent for spinocerebellar ataxia. 1-(3-(2-(1-benzothiophen-5-yl)ethoxy)propyl)azetidin-3-ol or a salt thereof has an effect of suppressing brain atrophy, in particular, cerebellar atrophy, and thus is useful as a prophylactic or therapeutic agent for spinocerebellar ataxia. Hence, it is possible to prevent or treat cerebellar atrophy observed in spinocerebellar ataxia by administering 1-(3-(2-(1-benzothiophen-5-yl)ethoxy)propyl)azetidin-3-ol or a salt thereof.
