The present invention provides a compound represented by the following formula (I): wherein: Ring A represents an optionally substituted piperazine ring, an optionally substituted morpholine ring, or an optionally substituted bomopiperazine ring; R
1 and R
2 are the same or different from each other, and represent a hydrogen atom or optionally substituted lower alkyl; R
3 and R
4 are the same or different from each other, and represent a hydrogen atom or halogenated or non-halogenated lower alkyl; R
3 to R
7 are the same or different from each other, and represent a hydrogen atom, hydroxy, optionally substituted lower alkyl, optionally substituted lower alkenyl, optionally substituted lower alkoxy, optionally substituted cycIoaJkyl, optionally substituted aryl, an optionally substituted aromatic heterocyclic ring, optionally substituted amino, or acyl; and represents a single bond or double bond, wherein R
2 and R
3 do not exist when carbon atoms respectively adjacent to R
2 : and R
3 form a double bond, and there is no case where all of R
1 to R
7 are hydrogen atoms, and R
1 and R
2 ; may form a ring together with an adjacent carbon atom; or a salt thereof.