A compound represented by formula: or its pharmaceutically acceptable salt, wherein L is NR 2 R 3 , SR 7 , SO 2 R 8 , substituted or unsubstituted alkyl, or substituted or unsubstituted alkenyl； R 2 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like； R 3 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like； R 7 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like； R 8 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like, provided that R 8 is not unsubstituted methyl or trifluoromethyl； Y is substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, or the like, provided that Y is not unsubstituted methyl or unsubstituted ethyl； Z is -CR 6 =, or -N=； R 1 is hydrogen, or substituted or unsubstituted alkyl； R 4 , R 5 and R 6 are each independently hydrogen, halogen, hydroxy, cyano, nitro, carboxy, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like.
