A diazepine derivative having the following formula (III) or a pharmacologically acceptable salt thereof is used as A P2X 4 receptor antagonist: wherein each of R 21 and R 22 is hydrogen, a C 1-8 alkyl group or the like R 23 is hydrogen, a C 1-8 alkyl group or the like each of R 24 and R 25 is hydrogen, a C 1-8 alkyl group or the like R 26 is hydrogen, a C 1-8 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 and p is 0 or 1.
