Novel fused polycyclic heterocycle derivatives having excellent antitumor effects and a process for producing the same. A compound represented by the following general formula (I) or pharmacologically acceptable salts thereof: ##STR1## wherein the ring A represents an optionally substituted monocyclic aromatic ring or a dicyclic fused ring in which at least one of the rings is an aromatic ring; the ring B represents pyrrole, 4H-1,4-oxazine, 4H-1,4-thiazine or 4(1H)-pyridone; the ring C represents an optionally substituted, monocyclic or dicyclic fused aromatic ring; and Y represents a group represented by the formula --e--f (wherein e represents a lower alkylene; and f represents amidino, guanidino or amino optionally substituted by optionally hydroxylated or optionally lower-alkylaminated lower alkyl;provided that the cases where the rings A and B are both optionally substituted monocyclic aromatic rings are excluded. Which has an excellent antitumor activity.