The present invention is related to a compound represented by formula (I) wherein —X— is —NH— or —S—; —Z— is —O— or —S—; R3, R5 and R6 are each independently a hydrogen atom, substituted or unsubstituted alkyl, or the like; R7 is a cyano, substituted or unsubstituted amino, or the like; R7′ is each independently a halogen; b is 0 or 1; or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition comprising thereof.