To provide a strain-proof sheet which is attached to the face cover, the back cover, etc. of a booklet which cannot be made to stand against a book case etc. due to the weak nerve and feebleness of the face cover and the back cover, and also, attached to the face cover, the back cover, etc. of the booklet, a file, a note, etc. whose face cover and back cover tend to buckle or yield with the lapse of time, when they are made to stand against the book case etc. for a long time.

The strain-proof sheet can be manufactured in the following way. First, the sheet which serves as a base is divided into an almost quadrilateral shape or an almost round shape or an almost elliptical shape, and the divided sheet is further redivided or used as it is. After that, an adhesive is applied to the sheet piece which is redivided or used as it is, and a release paper is applied to one side of the sheet to which the adhesive is applied.