Novel bicyclic heterocyclic sulfonamide and sulfonic ester derivatives represented by general formula (I) having an antitumor activity and a reduced toxicity, pharmacologically acceptable salts thereof, and a process for producing the same; wherein ring A represents an optionally substituted mono- or bicyclic aromatic group; ring B represents an optionally substituted 6-membered unsaturated hydrocarbon ring or 6-membered unsaturated heterocyclic group containing one nitrogen atom; ring C represents an optionally substituted 5-membered heterocyclic group containing one or two nitrogen atoms; W represents a single bond or -CH=CH-; X represents -NR¹- or oxygen; Y represents carbon or nitrogen; Z represents -NR²- or nitrogen; and R¹ and R² represent each independently hydrogen or lower alkyl.