An extended branching device, comprising: first branching means comprising a first port coupled to a first terminal station and adapted to receive a wavelength division multiplex, WDM, signal transmitted by the first terminal station, a second port coupled to a second terminal station, a third port, a fourth port, and a switch (111, 112) to couple the first port with one of the second port and the third port and couple the second port with the fourth port; second branching means comprising a fifth port coupled to the third port and adapted to receive the WDM signal transmitted by the first terminal station, a sixth port coupled to the fourth port, a seventh port coupled to a third branching means, and a first separating means (121, 123) for outputting, to the sixth port, a light signal of a first wavelength among the wavelengths inputted from the fifth port and outputting, to the seventh port, the other wavelengths inputted from the fifth port; wherein the second branching means is configured to be separable from the first branching means and; the third branching means, disposed between the second branching means and the third terminal station, comprising a ninth port coupled to the seventh port, a tenth port coupled to an eighth port of the second branching means, an eleventh port coupled to the third terminal station, and a second separating means for outputting to the tenth port a light signal of a second wavelength among the wavelengths inputted from the ninth port and outputting to the eleventh port a light signal of a third wavelength among the wavelengths inputted from the ninth port, wherein the third branching means is configured to be separable from the first branching means and the second branching means. first branching means comprising a first port coupled to a first terminal station and adapted to receive a wavelength division multiplex, WDM, signal transmitted by the first terminal station, a second port coupled to a second terminal station, a third port, a fourth port, and a switch (111, 112) to couple the first port with one of the second port and the third port and couple the second port with the fourth port; second branching means comprising a fifth port coupled to the third port and adapted to receive the WDM signal transmitted by the first terminal station, a sixth port coupled to the fourth port, a seventh port coupled to a third branching means, and a first separating means (121, 123) for outputting, to the sixth port, a light signal of a first wavelength among the wavelengths inputted from the fifth port and outputting, to the seventh port, the other wavelengths inputted from the fifth port; wherein the second branching means is configured to be separable from the first branching means and; the third branching means, disposed between the second branching means and the third terminal station, comprising a ninth port coupled to the seventh port, a tenth port coupled to an eighth port of the second branching means, an eleventh port coupled to the third terminal station, and a second separating means for outputting to the tenth port a light signal of a second wavelength among the wavelengths inputted from the ninth port and outputting to the eleventh port a light signal of a third wavelength among the wavelengths inputted from the ninth port, wherein the third branching means is configured to be separable from the first branching means and the second branching means.