A power over fiber system (1A, 1, 1B) comprising: a first data communication device including a power sourcing equipment device including a semiconductor laser configured to oscillate with electric power, thereby outputting feed light; a second data communication device including a powered device including a photoelectric conversion element configured to convert the feed light into electric power, the second data communication device configured to perform optical communication with the first data communication device; and an optical fiber cable (200A, 200, 200B) including a first end (201A, 201) connectable to the first data communication device and a second end (202A, 202) connectable to the second data communication device to transmit the feed light and signal light, wherein the first data communication device is capable of controlling low power supply and high power supply that are performed by the power sourcing equipment device, feed electric power by the high power supply exceeding feed electric power by the low power supply, wherein the first data communication device enables the high power supply after starting the low power supply to the second data communication device and receiving, from the second data communication device, a start signal indicating that a photoelectric-conversion-and-optical-communication unit (310, 320, 330, 360) of the second data communication device has started, and wherein the photoelectric-conversion-and-optical-communication unit includes the powered device, and is configured to start and transmit the start signal to the first data communication device when receiving the low power supply, and to enable extension of a number of target devices that receive electric power from the powered device when receiving the high power supply. a first data communication device including a power sourcing equipment device including a semiconductor laser configured to oscillate with electric power, thereby outputting feed light; a second data communication device including a powered device including a photoelectric conversion element configured to convert the feed light into electric power, the second data communication device configured to perform optical communication with the first data communication device; and an optical fiber cable (200A, 200, 200B) including a first end (201A, 201) connectable to the first data communication device and a second end (202A, 202) connectable to the second data communication device to transmit the feed light and signal light, wherein the first data communication device is capable of controlling low power supply and high power supply that are performed by the power sourcing equipment device, feed electric power by the high power supply exceeding feed electric power by the low power supply, wherein the first data communication device enables the high power supply after starting the low power supply to the second data communication device and receiving, from the second data communication device, a start signal indicating that a photoelectric-conversion-and-optical-communication unit (310, 320, 330, 360) of the second data communication device has started, and wherein the photoelectric-conversion-and-optical-communication unit includes the powered device, and is configured to start and transmit the start signal to the first data communication device when receiving the low power supply, and to enable extension of a number of target devices that receive electric power from the powered device when receiving the high power supply.