To provide an automatic bookbinding unit assembled in one piece for binding a document, which is of a simple composition and can perform a bookbinding process, simply and rapidly, by a user himself whenever his required document needs to be bound into a book style, without the use of special auxiliary equipment.

This automatic bookbinding unit consists of a front cover body 10 assembled in one piece with a front cover 12, a spine cover 14 and a back cover 16, an elastic clamp 20 of U groove-shape attached to the spine cover 14 and a rigid and/or spring-energized slider 30 of U groove shape which is inserted into the clamp 20 and keeps the upper edge parts 22a, 22b of the clamp 20 separated from each other. The elastic gripping force of both upper edge parts 22a, 22b of the clamp 20 is set to the level of a force strong enough to fix a document to be inserted into the clamp 20 semipermanently. Besides, the clamp 20 and the slide 30 are formed of a metal or a plastic material, and should be of the almost same length as the front cover body 10.