To provide a novel furanone derivative, and a medicine including the same. The furanone derivative is represented by the formula (I): wherein A represents -COOR1 or a hydrogen atom； R1 represents a hydrogen atom, an optionally substituted hydrocarbon group, or an optionally substituted heterocycle； R2 and R3 are the same or different and each independently represent a hydrogen atom, an optionally substituted hydrocarbon group, an optionally substituted phenyl group, an optionally substituted heterocycle, an optionally substituted heterocyclic fused ring, or an optionally substituted amino group； or alternatively, R2 and R3, taken together with the nitrogen atom to which they are attached, may form an optionally substituted heterocycle or an optionally substituted heterocyclic fused ring； and R4 represents a hydrogen atom or a halogen atom； with the proviso that when A represents -COOR1, R2 and R3 are not optionally substituted amino groups at the same time, and when A represents a hydrogen atom, R3 represents a hydrogen atom.
