To provide a bookmark, attached to a document, such as a book, a notebook or the like which is bound through bookbinding, while the same is slipped out or inserted automatically by the opening and closing of the document, in order to resolve the defect of the bookmark that the same is slipped out or loosed since the same is separated from the book.

A thick paper A, B, C, D is provided with a mountain fold 1 and valley folds 2 to form the bookmark having a three-dimensional form whereby the bookmark, which will not be hazardous when the book is opened and which will be pinched when the book is closed while which will be released when the book is opened, is prepared.