Abstract: A broad-band signal transmitting device including a signal transmitting transformer of the primary to secondary turn ratio 1 : N, comprising a first circuit for expanding the transmission band to low frequencies by decreasing the impedance as well as by decreasing the gain for the signal component in the primary circuit of the transmission transformer, a second circuit connected with the output side of the transmission transformer having an impedance larger than N.sup.2 times of the impedance of the primary side and smaller than the impedance exhibited by the stray capacitance of the secondary side at the upper limit of the transmission band, an amplifier for recovering the gain drop in the first circuit, and a low frequency compensating circuit for compensating the lack of low frequency transmission characteristic due to the transmission transformer.