A diazepine derivative having the following formula (III) or a pharmacologically acceptable salt thereof is used as A P2X4 receptor antagonist:wherein each of R21 and R22 is hydrogen, a C1-8 alkyl group or the likeR23 is hydrogen, a C1-8 alkyl group or the likeeach of R24 and R25 is hydrogen, a C1-8 alkyl group or the likeR26 is hydrogen, a C1-8 alkyl group, a halogen atom, hydroxyl, nitro, cyano, phenyl optionally having one or more substituents, or a heterocyclic group optionally having one or more substituents or the like andp is 0 or 1.
