A compound, which has a melanin-concentrating hormone antagonistic action and useful as an agent for preventing or treating obesity, and which is represented by the formula: wherein Ar is a cyclic group optionally having substituent(s); X is a bond or a spacer having a main chain of 1 to 6 atoms; R1 and R2 are the same or different and each is a hydrogen atom or a hydrocarbon group optionally having substituent(s), or R1 and R2 may form, together with the adjacent nitrogen atom, a nitrogen-containing heterocycle optionally having substituent(s); Y is a divalent hydrocarbon group optionally having substituent(s) (except CO); R3 is a hydrogen atom or a hydrocarbon group optionally having substituent(s); and ring A and ring B may further have substituents, and when ring B further has a substituent, the substituent may be linked to R1 to form a ring, or a salt thereof, or a prodrug thereof, is provided.