Disclosed are: a compound which can impart a high accumulation property in the blood, high stability in the blood and excellent target cell tropism to a substance of interest a complex of the compound and a substance of interest and an aggregate comprising the complex. Specifically disclosed is a conjugate composed of mannose 6-phosphate bound to one terminus of a polyethylene glycol chain. Also specifically disclosed is a complex which is compose of a substance of interest modified with a conjugate composed of mannose 6-phosphate bound to one terminus of a polyethylene glycol chain. Further specifically disclosed is an aggregate composed of substances of interest associated or aggregated to each other, wherein the conjugate is bound to at least a part of the aggregate.
