Steroid sulfatase inhibitors containing as the active ingredient estra-1,3,5(10)-triene derivatives represented by the following general formula (I) or pharmacologically acceptable salts thereof: (I) wherein R?1 and R2¿ are the same or different and each represents hydrogen, lower alkyl, etc.; R3 represents hydrogen, etc.; R4 represents hydrogen, etc.; R5 represents hydrogen, etc.; and R6 represents cyano, amino, COR53 (wherein R53 represents substituted lower alkyl, etc.), optionally substituted aryl, an optionally substituted heterocycle, etc.