A signal transfer device includes a signal transmitter, a first amplitude adjustment component, an adjustment signal output component, a detector and a second amplitude adjustment component. The signal transmitter outputs signals to first and second transfer paths based on single-phase or differential input signal. The first amplitude adjustment component 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 component outputs adjustment signals to the first and second transfer paths. The detector detects the adjustment signals. The second amplitude adjustment component 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.