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—SO
2
—Y′ (wherein Y′ is optionally substituted aryl or optionally substituted alkyl), and
R
1
to R
9
are each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted alkoxy or the like).