Abstract: An optical shunt device in which a pair of connecting ends (22, 23) for being connected to optical communication fiber sections (11) are divided into three systems. The first of the three systems is a passing-through light conduction path (19) through which light signals in two opposite directions are allowed to pass through between the connecting ends. The second of the three systems is a receiving light conduction path (20) having a first light-receiving end (20a) and a second light-receiving end (20b) each receiving a light signal from the connecting ends (22, 23). The third light path (21) has a first light-transmitting end (21a) and a second light-transmitting end (21b) each transmitting a light signal to the connecting ends.