To make a document binder unremovable easily, and eliminate the necessity to remove the document binder from documents when bound documents are to be recycled as recycled paper by a method wherein a male part having a head part and a solid shaft part, and a female part having a head part and a hollow shaft part are formed of a water-soluble resin respectively.

A binder 1 comprises a male part 2 and a female part 3, and either one of them is an injection-molded article of a resin of which the major component is a water-soluble and thermoplastic denatured polyvinyl alcohol, and the male part 2 has a shaft-form, and comprises a solid shaft part 21 and a head part 22 of a thicker diameter, and the female part has a tubular form, and comprises a hollow shaft part 31 having a shaft hole 33 and a head part 32 of a thicker diameter. When the shaft 21 of the male part 2 is wet with water and pushed into the shaft hole 33, the outer peripheral surface of the solid shaft part 21 of the male part 2 and a part being wet with water on the inner peripheral surface of the shaft hole 33 of the female part 3 are welded and integrated, and the male part 2 becomes unremovable. For documents 4, there is no fear that the male part 2 may be removed, and the documents 4 may be spread, and also, since the binder is water-soluble, a regenerating process is possible while the documents are being bound.