A submount is used for disposing an illuminant element or a light-receiving element having an optical axis. The submount is disposed at a plane and has a main body. The main body includes a first surface and a second surface. The first surface is approximately parallel to the plane and far away from the plane. The second surface is approximately parallel to the plane and adjacent to the plane. A disposing part of the first surface is tilted with respect to the second surface at a predetermined angle. The illuminant element or the light-receiving element is disposed on the disposing part. The optical axis of the illuminant element or the light-receiving element is tiled with respect to a normal of the second surface at the predetermined angle.