The present invention relates to a compound represented by formula (I): wherein R<；SUP>；1 <；/SUP>；represents a C1-3 alkyl group, R<；SUP>；2 <；/SUP>；represents a hydrogen atom or a C1-3 alkyl group, Ar represents a phenyl group or the like which may be substituted with 1 to 3 substituents, X represents an oxygen atom or the like, n and m are the same or different and integers of 0 to 2, or a pharmacologically acceptable salt, and use thereof as a medicament.
