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 bromopiperazine ring; R1 and R2 are the same or different from each other, and represent a hydrogen atom or optionally substituted lower alkyl; R3 and R4 are the same or different from each other, and represent a hydrogen atom or halogenated or non-halogenated lower alkyl; R3 to R7 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 cycloalkyl, optionally substituted aryl, an optionally substituted aromatic heterocyclic ring, optionally substituted amino, or acyl; and represents a single bond or double bond, wherein R2 and R3 do not exist when carbon atoms respectively adjacent to R2: and R3 form a double bond, and there is no case where all of R1 to R7 are hydrogen atoms, and R1 and R2; may form a ring together with an adjacent carbon atom; or a salt thereof.