PURPOSE: To attain a high power supply backup function and low prices by reducing power consumption at the stand-by state of a subscriber's line terminal in an optical subscriber system connecting a subscriber to a communication equipment such as an exchange and a transmitter through optical fibers and capable of transmitting/ receiving an optical signal.

CONSTITUTION: In the subscriber's optical terminal equipment 80, a backup battery 42 for the countermeasure against service interruption is built in a power supply block and a feeding route is divided into a normal feeding route A and a feeding route B to be used after detecting a call/terminating call. When a detection part 50 detects a terminating call signal to its own equipment which is received from a receiving part 22 and a detection part 35-3 detects a call, a feed switch 431 is turned on by a control signal to supply a current to the route B. Consequently power consumption in a stand-by state can sharply be reduced and the battery 42 can be functioned as a sufficiently effective back-up power supply at the time of service interruption though it is compact. An wavelength multiplex signal or a time-division multiplex signal can also be used as an optical signal to be transmitted between a communication equipment and the terminal equipment and the backup battery 42 can also be used as a backup power supply or a main power supply for the terminal equipment.