A JNK inhibitor containing a compound having an isoquinolinone skeleton or a salt thereof, such as a compound represented by the formula wherein ring A and ring B are each an optionally substituted benzene ring, X is —O—, —N═, —NR3— or —CHR3—, R2 is an acyl group, an optionally esterified or thioesterified carboxyl group, an optionally substituted carbamoyl group or an optionally substituted amino group and the like, a broken line shows a single bond or a double bond, and R1 is a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted heterocyclic group and the like, and the like.