To equip an optical wavelength dividing multiplexing system with a variable optical band-pass filter, and to provide an apparatus to change the center wavelength and the band width of an optical-band pass filter according to an optical wavelength band to be transmitted, and a method of controlling the apparatus. An optical wavelength multiplexing device 100 includes a CPL (multiplexing portion) 3 that multiplexes optical signals and outputs the multiplexed signal, a BPF (optical band-pass filter) 9 that is capable of changing its center wavelength and band width and receives an optical multiplex signal output by the multiplexing portion and lets the received optical multiplex signal pass therethrough, a storage portion that stores wavelength band control information 4 specifying the center wavelength and the band width, and a control portion that controls the center wavelength and the band width of the BPF 9 based on the wavelength band control information 4. The control circuit 10 controls the center wavelength and the band width of the BPF 9 based on the wavelength band control information 4.