An optical transceiver of the present invention comprising an OSA, a circuit board, and a flexible substrate connecting these, in which the flexible substrate has high-speed signal lines and other lines other than the high speed signal lines provided separated from each other on the same surface, a ground layer placed apart and opposite these, and a resistive layer placed apart and opposite the high-speed signal lines, the other lines and the ground layer. High-speed signal and the resistive layer are opposite at least a part of the other lines.