A transmission circuit includes a plurality of transmission lines connected in a ring to propagate signals among a plurality of devices. The plurality of transmission lines have a predetermined same propagation delay, and a predetermined transmission line impedance, and the predetermined transmission line impedance is a half or less of an output impedance of each of the plurality of devices. When a signal outputted from a first optional one of the plurality of devices is propagated to the plurality of devices other than the first optional device, the signal outputted from the first optional device exceeds a predetermined threshold of a signal voltage at a same time.