A signal transmission device comprising: - a plurality of optical receivers (5, 6) adapted to generate reception electric signals (E1, E2) from a plurality of reception optical signals (D1, D2) respectively including a plurality of carrier signals; - an extracting section adapted to extract reception data (F1 - F10) from the reception electric signals (E1, E2); and - a monitoring section adapted to send a notification signal for notifying of a carrier signal in a non-link-establishable state to the extracting section when any of the plurality of carrier signals is in the non-link-establishable state, wherein the extracting section includes: - a first signal extracting unit adapted to extract the reception data (F1 - F10) from the reception electric signals (E1, E2) at a first data transmission rate when a data transmission rate by the plurality of reception optical signals is the first data transmission rate; - a second signal extracting unit adapted to extract the reception data from the reception electric signals at a second data transmission rate when the data transmission rate by the plurality of reception optical signals is the second data transmission rate lower than the first data transmission rate; and - a reception signal switching section (76, 71, 74, 75), wherein: when the plurality of carrier signals of the plurality of reception optical signals are in a link-establishable state, the reception signal switching section (76, 71, 74, 75) adapted to supply the reception electric signals (E1, E2) generated by the plurality of optical receivers (5, 6) to the first signal extracting unit and output the reception data extracted by the first signal extracting unit, and when any of the plurality of carrier signals of the plurality of reception optical signals is in the non-link-establishable state, the reception signal switching section (76, 71, 74, 75) is adapted to supply the reception electric signals generated by the optical receivers using a carrier signal in the link-establishable state among the plurality of carrier signals of the reception optical signals to the second signal extracting unit and output the reception data extracted by the second signal extracting unit. - a plurality of optical receivers (5, 6) adapted to generate reception electric signals (E1, E2) from a plurality of reception optical signals (D1, D2) respectively including a plurality of carrier signals; - an extracting section adapted to extract reception data (F1 - F10) from the reception electric signals (E1, E2); and - a monitoring section adapted to send a notification signal for notifying of a carrier signal in a non-link-establishable state to the extracting section when any of the plurality of carrier signals is in the non-link-establishable state, - a first signal extracting unit adapted to extract the reception data (F1 - F10) from the reception electric signals (E1, E2) at a first data transmission rate when a data transmission rate by the plurality of reception optical signals is the first data transmission rate; - a second signal extracting unit adapted to extract the reception data from the reception electric signals at a second data transmission rate when the data transmission rate by the plurality of reception optical signals is the second data transmission rate lower than the first data transmission rate; and - a reception signal switching section (76, 71, 74, 75), when the plurality of carrier signals of the plurality of reception optical signals are in a link-establishable state, the reception signal switching section (76, 71, 74, 75) adapted to supply the reception electric signals (E1, E2) generated by the plurality of optical receivers (5, 6) to the first signal extracting unit and output the reception data extracted by the first signal extracting unit, and when any of the plurality of carrier signals of the plurality of reception optical signals is in the non-link-establishable state, the reception signal switching section (76, 71, 74, 75) is adapted to supply the reception electric signals generated by the optical receivers using a carrier signal in the link-establishable state among the plurality of carrier signals of the reception optical signals to the second signal extracting unit and output the reception data extracted by the second signal extracting unit.