[Purpose] The present invention provides compounds useful as agents for the prevention or treatment of a sex hormone-dependent disease or the like.[Solution] The present invention provides nitrogen-containing fused ring derivatives represented by the following general formula (I) which has a GnRH antagonistic activity, prodrugs, salts, pharmaceutical compositions containing the same, medicinal uses thereof and the like. In the formula (I), rings A and B are independently aryl or heteroaryl; RA and RB are independently halogen, cyano, alkyl, alkylsulfonyl, —OW1, —SW1, —COW2, —NW3W4, —SO2NW3W4, aryl, etc.; RC is H or alkyl; E is oxygen atom, etc.; U is single bond or alkylene; and X is Y, —CO—Y, —SO2—Y, —S-(alkylene)-Y, —O-(alkylene)-Y, —SO2-(alkylene)-Y, etc.; Y is Z or amino, etc.; and Z is cycloalkyl, heterocycloalkyl, aryl, heteroaryl, etc.