A CTGF expression inhibitor comprising a compound of the formula I:
a pharmaceutically acceptable salt or solvate thereof as an active ingredient,
(wherein Y is hydroxy or a group of the formula: -NH-SO2-Y' (wherein Y' is optionally substituted aryl or optionally substituted alkyl), and
R1 to R9 are each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted alkoxy or the like).