The present invention relates a variable optical multiplexer/demultiplexer which can be made smaller and can restrain characteristics from deteriorating. The optical multiplexer/demultiplexer comprises a first optical system, a wavelength branching device, a second optical system, and an optical path changing part. The optical multiplexer/demultiplexer has a plurality of input/output ports, and the first optical system, the wavelength branching device, and the second optical system are disposed between the ports and the optical path changing part. When light is fed into any of the ports, individual wavelength components included in the light are outputted from any of the ports. The optical path changing part inputs the wavelength components condensed by the second optical system, and output the wavelength components to an output optical path which is parallel to but not on the same line as the input optical paths of the wavelength components.