Abstract: A fluorescent probe for sialidase activity detection, is a compound represented by the following general formula or a salt thereof. R1, if present, represents the same or different monovalent substituent present on a benzene ring. R2 and R3 each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen atom. R4 and R5 each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen atom. R6 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a fluorinated alkyl group having 1 to 5 carbon atoms. R6? represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R6? may form, together with R3 or R5 a five to seven-membered heterocyclyl or heteroaryl containing a nitrogen atom to which R6? is bonded.