A signal transmission circuit includes a primary element configured to receive differential signals which are generated from a transmission signal and contain alternating-current (AC) components, a secondary element magnetically or capacitively coupled with the primary element and configured to output AC signals containing the AC components of the differential signals, a secondary circuit including a pair of transmission lines configured to propagate the AC signals. The secondary circuit is electrically connected to the secondary element and extracts the transmission signal from the AC signals. The feedback circuit feedbacks an intermediate voltage between voltages of the pair of transmission lines such that the intermediate voltage is converged to a reference voltage. This signal transmission circuit prevents the secondary circuit from malfunctioning due to noise.