POLYGLYCERIN DERIVATIVE

Provided is a polyglycerin derivative which can be used usefully as a draw solute in a membrane separation method using a forward osmosis membrane. A polyglycerin derivative having a repeating unit represented by general formula (I) [wherein GL represents a glycerin residue; X represents an alkylene group having a carbonyl bond (-CO-) as a linking group on the GL side and having 1 to 10 carbon atoms; AO represents an alkyleneoxy group having 1 to 10 carbon atoms; n is the number of moles of AO added and represents a numerical value of 0 or 1; and R represents at least one member selected from a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a 3- to 10-membered cycloalkyl group, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 12 carbon atoms and an acyl group having 1 to 11 carbon atoms].