To provide a document binder that allows very easy filing of periodicals such as newspapers.

Each binding thread 11 inserted into punched holes of a document A is made as a double-face fastener. Locking pieces 10 provided on a front cover 2 and a back cover 3 are respectively formed with a thin-groove-shaped hooking part 13. A bonded inside-cover piece 15 is provided along the locking piece 10, thereby allowing very easy bookbinding. The inside-cover piece 15 is pasted to the whole locking piece 10 above the binding threads 11, allowing the tensile force of the binding threads 11 to be maintained for a long period of time.