The present invention relates to a compound represented by formula [I]: wherein: R1 is hydrogen, halogen, lower alkyl or cyano； Ring A is an optionally substituted heterocyclic group； Ring B is an optionally substituted 3 to 6-membered monocyclic group； and Y is optionally substituted amino, optionally substituted cyclic amino, optionally substituted aliphatic 3 to 6-membered monocyclyloxy, optionally substituted lower alkyl or optionally substituted lower alkyl-O&mdash；, or a pharmaceutically acceptable salt thereof, and to their use as PDE10 inhibitor.
