An optical submarine branching apparatus includes a first, second, and third switching unit. The first switching unit is connected to N first, second, and third optical fiber transmission lines connected to a first, second and third terminal stations, respectively, and switches a transmission route for a wavelength-multiplexed optical signal. The second switching unit is interposed on the N first optical fiber transmission lines between the first terminal station and the first switching unit, and switches a connection relation between in front of and behind a place where the second switching unit is interposed. The third switching unit is interposed on the N second optical fiber transmission lines between the second terminal station and the first switching unit, and switches a connection relation between in front of and behind a place where the third switching unit is interposed.