A substrate on which cavities having floors and steps is provided. End faces of a light-emitting device, an optical component, and an optical transmission line are abutted on one of the cavity for positioning, and end faces of a light-receiving device, an optical component, and an optical transmission line are also abutted on the other cavity for positioning. Integrated alignment of optical axes facilitates alignment of optical axes, and thus eliminates the need of a CAN package. Accordingly, the size and height of an optical communications module can be reduced.