An optical line terminal (OLT) of a passive optical network (PON) detects a fault in an optical path configured as a single optical fiber core having an annular shape, divides the optical path into a right path and a left path having bi-directionality based on the fault position in which the fault has occurred, demultiplexes a plurality of downstream optical wavelength signals to be transmitted to at least one optical network terminal (ONT) of each group into an optical wavelength signal of the right path and an optical wavelength signal of the left path according to the position in which the fault has occurred, and outputs the same to at least one of the ONTs of each group.