The first and second light-emitting regions are provided on the light source. When the first optical fiber having the first core diameter is connected, the light emitted from the first light-emitting region enters the first core. When the second optical fiber having a greater core diameter than the first core diameter is connected, the lights emitted from the first and second light-emitting regions enter the second core. It is thus possible to connect the optical transmission device with multiple optical fibers having different core diameters. It is thus possible to provide the optical transmission device and the communication device, which are low in cost and high in convenience.