The present invention relates to a compound represented by the general formula [I]: wherein Ar1 represents an aryl or heteroaryl group which may have a substituent selected from the group consisting of a halogen atom and lower alkyl, lower alkenyl, lower haloalkyl, lower alkoxy, lower alkylthio, lower alkylamino, lower dialkylamino, acyl and aryl groups; Ar2 represents an aryl or heteroaryl group which may have a substituent selected from the group consisting of a halogen atom and lower alkyl, lower alkenyl, lower haloalkyl, lower alkoxy, lower alkylthio, lower alkylamino, lower dialkylamino and aryl groups; n is zero, 1 or 2; and R1 and R2 may be the same or different and each represents a hydrogen atom or a lower alkyl group, or its salt, a method for its preparation as well as an agent for the treatment of bulimia, obesity or diabetes comprising it as an active ingredient.