A serial communication branching device and a serial communication system are provided. The serial communication branching device, which branches a plurality of slaves connected to the master by a daisy chain into a plurality of paths, is equipped with a first communication circuit that carries out communication with the master connected to a preceding stage side, a plurality of second communication circuits that carry out communication with the slaves of the paths connected to a subsequent stage side, and a path selection circuit disposed between the first communication circuit and the second communication circuits. In the case that a slave connected on the subsequent stage side transmits a reply signal to the master responsive to a transmission signal transmitted from the master, the path selection circuit selects a path of the slave that transmits the reply signal, and outputs the reply signal from the selected path to the master.