The invention provides a high-molecular-weight polyethylene glycol derivative that does not cause vacuolation of cells. The degradable polyethylene glycol derivative is represented by the following formula (1): wherein m is 1-7, n1 and n2 are each independently 45-682, p is 1-4, R is an alkyl group having 1-4 carbon atoms, Z is an oligopeptide with 2-8 residues composed of neutral amino acids excluding cysteine, Q is a residue of a compound having 2-5 active hydrogens, X is a functional group capable of reacting with a bio-related substance, and L1, L2, L3, L4 and L5 are each independently a single bond or a divalent spacer.