A powered device of an optical power supply system includes a photoelectric conversion element, a semiconductor laser for feedback and a control device. The photoelectric conversion element converts feed light into electric power, wherein the feed light is from a power sourcing equipment. The semiconductor laser oscillates with a portion of the electric power, thereby outputting feed light to a power supplying side. The control device monitors a power supply amount of the electric power to a load, and according to the power supply amount, controls an electricity-light conversion amount of conversion that is performed by the semiconductor laser.