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 homopiperazine 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；R5 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； andrepresents a single bond or double bond, or a salt thereof.
