A method for producing a narrowly distributed and high-purity polyalkylene glycol derivative having an amino group at an end, a polymerization initiator for use in the method, and a precursor of the polymerization initiator are provided.The present invention provides: a method for producing a polyalkylene glycol derivative having an amino group at an end, using, as a polymerization initiator, a compound represented by the general formula (I); a compound represented by the following general formula (I); and a precursor thereof: wherein RA1a and RA1b each independently represent a protective group of the amino group, or one of RA1a and RA1b represents H and the other represents a protective group of the amino group, or RA1a and RA1b bind to each other to represent a cyclic protective group forming a ring; RA2 represents a linear, branched, or cyclic hydrocarbon group having 1 to 6 carbon atoms; RA3 represents a single bond, or a linear, branched, or cyclic hydrocarbon group having 1 to 20 carbon atoms, and the hydrocarbon group may contain a heteroatom; the total number of carbon atoms (or the total number of carbon atoms and heteroatoms) of RA2 and RA3 is 4 or more; and M represents an alkali metal.