An optical transmission system includes an optical transmitting device (8) and an optical receiving device (9). The optical transmitting device (8) includes an operating channel transmitting unit (81) that transmits a first optical signal to an operating channel, and a redundant channel transmitting unit (82) that transmits a second optical signal having the same information as the first optical signal to a redundant channel. The optical receiving device (9) includes a local selection function unit (91) that has a function of selecting a wavelength of the first optical signal or the second optical signal transmitted from the optical transmitting device (8), a channel setting control unit (92) that sets a wavelength to be selected by the local selection function unit (91), and a receiving unit (93) that receives the first optical signal or the second optical signal having the wavelength selected by the local selection function unit (91).