A semiconductor laser and an optical fiber are optically coupled via a first lens and a second lens, the second lens is previously fixed to a module package and these parts are mounted to the module package, when focal lengths of the first lens and the second lens are respectively designated by f1 and f2, an optical distance between a principal plane of the first lens on its side of the second lens and a principal plane of the second lens on its side of the first lens, is made substantially equal to f1+f2. Thereby, there is provided an optical transmission module having low price capable of achieving a high coupling efficiency with high yield.