A folding roller (8, 10) in a folding device which is used for folding the flat object to be folded extends along a central axis (X-X) and is provided with a first axial part (30) and a second axial part (32). The first axial part is provided with a first surface (40) for folding the object to be folded. The second axial part (32) comprises a main relief printing plate (44) which radially dents relatively to the first folding surface (40). The folding roller is used in a knife type folding device.