A clip includes an insertion piece insertable into a valley formed by folding a corner of a stack of a plurality of paper pieces, a front-side clamping piece contactable with a paper piece portion on a front side of the valley, and a back-side clamping piece contactable with a paper piece portion on a back side of the valley. The insertion piece, front-side clamping piece, and back-side clamping piece are elastically and integrally formed so that the paper piece portion on the front side and the paper piece portion on the back side of the valley are clamped between the front-side clamping piece and the insertion piece and between the insertion piece and the back-side clamping piece, respectively, and both of the paper piece portion on the front side and the paper piece portion on the back side of the valley are clamped between the front-side and back-side clamping pieces.