When we construct a model of origami (a model of a folded sheet of paper) in a computer, it is usual to represent the model as a set of polygons having zero thickness. One of the typical characteristics of origami is that there are many instances where multiple faces are located on a same plane. In these cases, the usual z-buffer rendering method fails as multiple faces have the same depth. Furthermore, many penetrations between faces located close to each other frequently occur when the origami is folded almost flat. However, it is difficult to remove all such penetrations with moving or fixing the geometry of the model. In this paper, we propose a new rendering method that solves these problems one at a time by using the OR matrix. This is a matrix constructed from a crease pattern, and it represents the overlapping relation between every two faces. Key words: computer graphics, rendering, origami