An optical access system includes an optical transmission device and an optical reception device. In the optical access system, the optical transmission device includes: a signal generation unit that generates a plurality of optical signals by generating monitoring control signals including identical information in predetermined cycles and superimposing the monitoring control signal on a main signal each time generating the monitoring control signal; and a transmission unit that transmits the generated optical signals to the optical reception device. The optical reception device includes: a photoelectric conversion unit that converts the optical signals into electrical signals; an analog-to-digital converter that generates quantized data of a plurality of monitoring control signals by sampling a plurality of electrical signals including the plurality of monitoring control signals; an averaging processing unit that performs an averaging process on a plurality of pieces of the generated quantized data; and a demodulation unit that demodulates the monitoring control signals, using the plurality of pieces of the quantized data subjected to the averaging process.