A signal transfer device includes a signal transmitter, a first amplitude adjustment means, an adjustment signal output means, a detector and a second amplitude adjustment means. The signal transmitter outputs signals to first and second transfer paths based on single-phase or differential input signal. The first amplitude adjustment means adjusts at least one of amplitudes of the signals transferred to the first and second transfer paths based on a predetermined amplitude ratio. The adjustment signal output means outputs adjustment signals to the first and second transfer paths. The detector detects the adjustment signals. The second amplitude adjustment means adjusts at least one of the amplitudes of the signals transferred to the first and second transfer paths based on detection result of the detector.