An optical transmission system of the present invention includes input ports to which laser beams are respectively input, condensing, input optical elements, input reflectors corresponding one-to-one to the input optical elements each, output reflectors, output optical elements, and output ports. Assume that maximum one and minimum one of optical distances between the input optical elements and the output optical elements are DL and DS, respectively. Then, the beam waist position Q of the laser beam output from the input optical element closest to the input port satisfies a relation: 0.9(DL+DS)/4.ltoreq.Q.ltoreq.1.1(DL+DS)/4.