An optical apparatus receives an upward signal light from a plurality of subscriber units, where the upward signal light is composed of a plurality of time slots corresponding to the plurality of optical subscriber units. The optical apparatus includes a driving unit configured to determine a respective required gain for light from each of the plurality of optical subscriber units, an amplifying section configured to amplify the upward signal light with the required gain corresponding to the time slots of the upward signal light, and a receiver configured to receive the amplified upward signal light.