[wherein n represents an integer of from 1 to 4, R1 represents substituted or unsubstituted lower alkyl, -C(=Y)R9 or the like, R2 represents a hydrogen atom, substituted or unsubstituted lower alkyl or the like, R3 represents substituted or unsubstituted lower alkyl, substituted or unsubstituted aryl, a substituted or unsubstituted heterocyclic group or the like, and R4 represents halogen or the like.]
A phosphodiesterase 10A inhibitor which comprises a quinoline derivative represented by the above formula (I) or a pharmaceutically acceptable salt thereof as an active ingredient is provided.