Disclosed is an aryl-substituted nitrogen-containing heterocyclic compound represented by the formula (I) below or a pharmaceutically acceptable salt thereof. This compound serves as nociceptin receptor antagonist and is useful as a pharmaceutical agent for treating diseases associated with a nociceptin receptor. (I) [in the formula, A1, A2 and A3 independently represent a carbon atom or a nitrogen atom, and one or two of A1, A2 and A3 represent a carbon atom; R1 represents a lower alkyl group or the like; R2 represents a phenyl group which may be substituted with a halogen atom or the like; R3 represents a hydrogen atom, a lower alkyl group or the like; and R4 represents a lower alkyl group or the like.]