A technical configuration is proposed to implement a wavelength division multiplexing device with a more dense frequency interval between channels to a level less than 1/2 of the standard frequency interval by using an optical filter technology with a standard frequency interval. A wavelength division multiplexing apparatus according to the present invention comprises: a plurality of first optical filters having a predetermined frequency interval; and a plurality of second optical filters having the same predetermined frequency interval as that of the plurality of first optical filters, and having a passband offset by 1/2 of the predetermined frequency interval compared to the passband of the first optical filter optical filter; and an input part of the second optical filter corresponding to the passband frequency of the first optical filter is connected to the pass part of the first optical filter, and the optical signal primary separated from the first optical filter is received. The second optical filter is configured to separate again into optical signals of the pass section and the reflection section.
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