An optical transmission apparatus that improves optical transmission quality by performing an optical noise correction and optical level detection with great precision. A first optical amplifier performs optical amplification with an optical fiber transmission line as an amplification medium. A second optical amplifier inputs second excitation light into an amplification medium in which an active substance for optical amplification is doped to perform optical amplification. A first optical level detector monitors, before transmitting an optical signal, a level of optical noise scattered by the first optical amplifier by emitting first excitation light in an operating environment and detects an optical level at the time of transmitting the optical signal by subtracting the level of the optical noise from a signal amplified by the first optical amplifier. A second optical level detector monitors, before transmitting an optical signal, a level of optical noise emitted from the second optical amplifier by emitting the second excitation light in the operating environment and detects an optical level at the time of transmitting the optical signal by subtracting the level of the optical noise from a signal amplified by the second optical amplifier.