A composition of an agent for treating a precursor of a three-dimensional object for removing a support material from a precursor of the three-dimensional object containing a three-dimensional object and the support material, the composition containing water and a water-soluble compound having a solubility parameter (SP value) calculated by using the Fedors' method of 8 (cal/cm 3) 1/2 to 13 (cal/cm 3) 1/2, measured as defined in the description, and having a pH of 6 to 8; wherein a soluble material for three-dimensional modeling that is a raw material of the support material contains a polyester resin having a hydrophilic group and/or a polyamide resin having a hydrophilic group, and wherein the water-soluble compound is at least one type selected from the group consisting of the following formulas, and: wherein in the formula, R 1 is an alkyl group having 2 to 22 carbon atoms, a hydroxy group, a benzyl group, an acetyl group, or an acetoxy group; and X is an alkylene group having 1 to 12 carbon atoms that may have a hydroxy group or a m1 n1 group, wherein m1 is an average addition mole number of an oxyethylene group {-EO-} and an integer of 1 to 200, and n1 is an average addition mole number of an oxypropylene group {-PO-} and an integer of 0 to 50, R 2 is an alkyl group having 2 to 8 carbon atoms in a case R 1 is an alkyl group having 2 to 4 carbon atoms; R 2 is an alkyl group having 4 to 8 carbon atoms in a case R 1 is a hydroxy group and X is an alkylene group having 2 or 3 carbon atoms that has no hydroxy group; R 2 is an allyl group in a case R 1 is a hydroxy group and X is an alkylene group having 3 or 8 carbon atoms that has a hydroxy group; R 2 is an alkyl group having 2 to 8 carbon atoms in a case R 1 is an acetyl group, X is a m1 n1 group, wherein m1 is an integer from 1 to 4, and n1 is 0; and R 2 is a hydrogen atom in a case R 1 is a benzyl group or an alkyl group having 5 to 22 carbon atoms, X is a m1 n1 group, wherein m1 is an integer from 1 to 200, and n1 is 0 to 50, wherein in the formula, R 3 and R 4 are same or different; and R 3 and R 4 represent an alkyl group having 1 to 4 carbon atoms, wherein in the formula, R 6 and R 7 are same or different; and R 6 and R 7 represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. the composition containing water and a water-soluble compound having a solubility parameter (SP value) calculated by using the Fedors' method of 8 (cal/cm 3) 1/2 to 13 (cal/cm 3) 1/2, measured as defined in the description, and having a pH of 6 to 8; wherein a soluble material for three-dimensional modeling that is a raw material of the support material contains a polyester resin having a hydrophilic group and/or a polyamide resin having a hydrophilic group, and wherein the water-soluble compound is at least one type selected from the group consisting of the following formulas, and: wherein in the formula, R 1 is an alkyl group having 2 to 22 carbon atoms, a hydroxy group, a benzyl group, an acetyl group, or an acetoxy group; and X is an alkylene group having 1 to 12 carbon atoms that may have a hydroxy group or a m1 n1 group, wherein m1 is an average addition mole number of an oxyethylene group {-EO-} and an integer of 1 to 200, and n1 is an average addition mole number of an oxypropylene group {-PO-} and an integer of 0 to 50, R 2 is an alkyl group having 2 to 8 carbon atoms in a case R 1 is an alkyl group having 2 to 4 carbon atoms; R 2 is an alkyl group having 4 to 8 carbon atoms in a case R 1 is a hydroxy group and X is an alkylene group having 2 or 3 carbon atoms that has no hydroxy group; R 2 is an allyl group in a case R 1 is a hydroxy group and X is an alkylene group having 3 or 8 carbon atoms that has a hydroxy group; R 2 is an alkyl group having 2 to 8 carbon atoms in a case R 1 is an acetyl group, X is a m1 n1 group, wherein m1 is an integer from 1 to 4, and n1 is 0; and R 2 is a hydrogen atom in a case R 1 is a benzyl group or an alkyl group having 5 to 22 carbon atoms, X is a m1 n1 group, wherein m1 is an integer from 1 to 200, and n1 is 0 to 50, wherein in the formula, R 3 and R 4 are same or different; and R 3 and R 4 represent an alkyl group having 1 to 4 carbon atoms, wherein in the formula, R 6 and R 7 are same or different; and R 6 and R 7 represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.