A compound represented by formula: or its pharmaceutically acceptable salt, wherein L is NR2R3, SR7, SO2R8, substituted or unsubstituted alkyl, or substituted or unsubstituted alkenyl; R2 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like; R3 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like; R7 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like; R8 is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like, provided that R8 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 —CR6═, or —N═; R1 is hydrogen, or substituted or unsubstituted alkyl; R4, R5 and R6 are each independently hydrogen, halogen, hydroxy, cyano, nitro, carboxy, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, or the like.