An optical demultiplexing device (10, 110, 110a) comprising: first branch means configured to branch an optical signal in which signals having a plurality of wavelength intervals different from one another are multiplexed by the number of wavelength intervals; a plurality of band division means (12-1 to 12-M) arranged so as to correspond to the plurality of respective wavelength intervals, the plurality of band division means configured to generate, for each of the wavelength intervals, a band division signal in which a signal band of an optical signal branched by the first branch means is divided by a predetermined bandwidth and an odd channel and an even channel are separated from each other in each of the wavelength intervals; a plurality of multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N) arranged, for each of the signal bands that have been divided, so as to correspond to the odd channel and the even channel, the plurality of multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N) configured to multiplex, for each of the signal bands that have been divided, the band division signals, output from the band division means, including odd channels of the respective wavelength intervals, and configured to multiplex, for each of the signal bands that have been divided, the band division signals including the even channels of the respective wavelength intervals; a plurality of second branch means (14a-1 to 14a-N, 14b-1 to 14b-N) arranged, for each of the signal bands that have been divided, so as to correspond to the odd channel and the even channel, the plurality of second branch means (14a-1 to 14a-N, 14b-1 to 14b-N) configured to branch each of a multiplexed signal including odd channels of the respective wavelength intervals multiplexed by using each of the multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N) and a multiplexed signal including even channels of the respective wavelength intervals into a plurality of communication devices; and control means configured to control the band division means, wherein each of the plurality of band division means includes a wavelength selective switch (113a-1, 113b-1, 113a-2, 113b-2, 113a-3, 113b-3, 117-1, 117-2, 117-3) and the control means configured to control the wavelength selective switch based on information indicating a signal arrangement of the signals in the respective wavelength intervals in the optical signal, and configured to cause the wavelength selective switch to output a signal of a wavelength band in which a signal of a corresponding wavelength interval is present to the multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N), and to cause the wavelength selective switch to cut off a signal of a wavelength band in which a signal of the corresponding wavelength interval is not present. first branch means configured to branch an optical signal in which signals having a plurality of wavelength intervals different from one another are multiplexed by the number of wavelength intervals; a plurality of band division means (12-1 to 12-M) arranged so as to correspond to the plurality of respective wavelength intervals, the plurality of band division means configured to generate, for each of the wavelength intervals, a band division signal in which a signal band of an optical signal branched by the first branch means is divided by a predetermined bandwidth and an odd channel and an even channel are separated from each other in each of the wavelength intervals; a plurality of multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N) arranged, for each of the signal bands that have been divided, so as to correspond to the odd channel and the even channel, the plurality of multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N) configured to multiplex, for each of the signal bands that have been divided, the band division signals, output from the band division means, including odd channels of the respective wavelength intervals, and configured to multiplex, for each of the signal bands that have been divided, the band division signals including the even channels of the respective wavelength intervals; a plurality of second branch means (14a-1 to 14a-N, 14b-1 to 14b-N) arranged, for each of the signal bands that have been divided, so as to correspond to the odd channel and the even channel, the plurality of second branch means (14a-1 to 14a-N, 14b-1 to 14b-N) configured to branch each of a multiplexed signal including odd channels of the respective wavelength intervals multiplexed by using each of the multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N) and a multiplexed signal including even channels of the respective wavelength intervals into a plurality of communication devices; and control means configured to control the band division means, wherein each of the plurality of band division means includes a wavelength selective switch (113a-1, 113b-1, 113a-2, 113b-2, 113a-3, 113b-3, 117-1, 117-2, 117-3) and the control means configured to control the wavelength selective switch based on information indicating a signal arrangement of the signals in the respective wavelength intervals in the optical signal, and configured to cause the wavelength selective switch to output a signal of a wavelength band in which a signal of a corresponding wavelength interval is present to the multiplexing means (13a-1 to 13a-N, 13b-1 to 13b-N), and to cause the wavelength selective switch to cut off a signal of a wavelength band in which a signal of the corresponding wavelength interval is not present.