Disclosed is a substance having an antagonistic effect on the binding ofhistamine to a histamine H3receptor or an inhibitory effect on the activity which a histamine H3 receptorconstantly exhibits. Acompound represented by the formula (I) or a pharmaceutically acceptable saltthereof； (I)(see formula I)wherein R1 represents a phenyl group which may be substituted or the like andR2 represents a cyanogroup which may be substituted or the like, or R1 and R2 together form analiphatic heterocylic ringwhich may be substituted； R3 represents a group represented by the formula (II-1) below；(see formula II-1)and all of X1 to X4 represent a carbon atom or the like: (II-1) where R4 andR5 represent a lower alkylgroup or the like； and ml represents an integer of 2 to 4.
