(wherein R represents a residue comprising a reactive group or a group capable of being transformed into the reactive group; n represents an integer of 3 or more; and X represents a residue capable of having the following structure by n in number: R1s each represent a hydrogen atom or a group capable of being transformed into a hydrogen atom, and 6 or more of R1s may be the same or different) The compound represented by the above formula (1), which is capable of modifying a physiologically active polypeptide or a derivative thereof, or a low molecular compound while maintaining the physiological activity, or which is useful for improving the stability or water-solubility of the low molecular compound, are provided.