There has been a need for coelenteramide analogs or the like that produce fluorescent proteins which exhibit different fluorescent characteristics from those of the existing fluorescent proteins. Disclosed is a compound represented by general formula (1) (wherein R1 represents a substituted or unsubstituted aryl, a substituted or unsubstituted arylalkyl, a straight or branched alkyl which may optionally be substituted with an alicyclic group, an alicyclic group or a heterocyclic group R2 represents hydrogen or —(SO2)R4 R3 represents hydrogen, hydroxyl, methoxy or acetoxy R4 represents a substituted or unsubstituted aryl, a substituted or unsubstituted arylalkyl or a straight or branched alkyl which may optionally be substituted with an alicyclic group and X1 represents —C(═S)— or —SO2—).
