A transmission device for suppressing the glass-fiber effect includes a circuit board and a transmission line. The circuit board includes a plurality of glass fibers, so as to define a fiber pitch. The transmission line is disposed on the circuit board. The transmission line includes a plurality of non-parallel segments. Each of the non-parallel segments of the transmission line has an offset distance with respect to a reference line. The offset distance is longer than or equal to a half of the fiber pitch.