A biofilm-removing agent which effectively removes biofilms is provided.A biofilm-removing agent containing a basic amino acid derivative represented by the following formula (1) or a salt thereof: (wherein R1 represents a linear- or branched-alkyl group having 4 to 18 carbon atoms or a linear- or branched-alkenyl group having 4 to 18 carbon atoms; X and Y each represent a group selected from the groups represented by the following formulas: and m represents an integer from 1 to 5).