A method for producing a multi-arm type polyethylene glycol derivative represented by the following formula, wherein the following step, step, step, step, and step are carried out in this order: wherein, in the formula, L is a group selected from the group consisting of a linear or branched alkylene group having 3 to 8 carbon atoms, a substituted or unsubstituted arylene group having 6 to 12 carbon atoms and a cycloalkylene group having 6 to 12 carbon atoms, k represents 1 or 2, n represents an average molar number of oxyethylene groups added and n represents an integer between 3 and 600, X represents an alkylene group which may have a single bond, an ester bond, a urethane bond, an amide bond, an ether bond, a carbonate bond, a secondary amino group, a urea bond, a thioether bond, or a thioester bond in a chain or at a terminal, and Y represents a chemically reactive functional group; Step: a step of protecting an even number of hydroxyl groups, while leaving only the hydroxyl group at the 1-position of a polyhydric alcohol having an odd number of hydroxyl groups, other than the hydroxyl group at the 1-position by cyclic benzylidene acetalization, Step: a step of linking two molecules of the compound obtained in the step to a compound represented by the following formula by an etherification reaction: A-L-A wherein, in the formula, L represents a group selected from the group consisting of a linear or branched alkylene group having 3 to 8 carbon atoms, a substituted or unsubstituted arylene group having 6 to 12 carbon atoms and a cycloalkylene group having 6 to 12 carbon atoms, and A represents a halogen atom selected from chlorine, bromine or iodine, or a sulfone-based leaving group, Step: a step of deprotecting the cyclic benzylidene acetal structure at the terminal of the compound obtained in the step, where 8 hydroxyl groups are formed in the case of k=1 and 12 hydroxyl groups are formed in the case of k=2, Step: a step of polymerizing 3 to 600 mol of ethylene oxide to each hydroxyl group of the compound obtained in the step to obtain a multi-arm type polyethylene glycol derivative, and Step: a step of functionalizing the hydroxyl group at the terminal of the multi-arm type polyethylene glycol derivative obtained in the step. L is a group selected from the group consisting of a linear or branched alkylene group having 3 to 8 carbon atoms, a substituted or unsubstituted arylene group having 6 to 12 carbon atoms and a cycloalkylene group having 6 to 12 carbon atoms, k represents 1 or 2, n represents an average molar number of oxyethylene groups added and n represents an integer between 3 and 600, X represents an alkylene group which may have a single bond, an ester bond, a urethane bond, an amide bond, an ether bond, a carbonate bond, a secondary amino group, a urea bond, a thioether bond, or a thioester bond in a chain or at a terminal, and Y represents a chemically reactive functional group; Step: a step of protecting an even number of hydroxyl groups, while leaving only the hydroxyl group at the 1-position of a polyhydric alcohol having an odd number of hydroxyl groups, other than the hydroxyl group at the 1-position by cyclic benzylidene acetalization, Step: a step of linking two molecules of the compound obtained in the step to a compound represented by the following formula by an etherification reaction: A-L-A wherein, in the formula, L represents a group selected from the group consisting of a linear or branched alkylene group having 3 to 8 carbon atoms, a substituted or unsubstituted arylene group having 6 to 12 carbon atoms and a cycloalkylene group having 6 to 12 carbon atoms, and A represents a halogen atom selected from chlorine, bromine or iodine, or a sulfone-based leaving group, L represents a group selected from the group consisting of a linear or branched alkylene group having 3 to 8 carbon atoms, a substituted or unsubstituted arylene group having 6 to 12 carbon atoms and a cycloalkylene group having 6 to 12 carbon atoms, and A represents a halogen atom selected from chlorine, bromine or iodine, or a sulfone-based leaving group, Step: a step of deprotecting the cyclic benzylidene acetal structure at the terminal of the compound obtained in the step, where 8 hydroxyl groups are formed in the case of k=1 and 12 hydroxyl groups are formed in the case of k=2, Step: a step of polymerizing 3 to 600 mol of ethylene oxide to each hydroxyl group of the compound obtained in the step to obtain a multi-arm type polyethylene glycol derivative, and Step: a step of functionalizing the hydroxyl group at the terminal of the multi-arm type polyethylene glycol derivative obtained in the step.