To prevent a filter from getting out of its path by performing transfer between filters when used through a transparent filter part of a filter array.

Transfer between two filters in a filter array comprising each filter that selects light of each wavelength which is transmitted as multiplexed data flow along an optical fiber is performed through nominally transparent filter parts of the filter array. Different filters 2 to 5 are mechanically provided on each arm of a cross-shaped glass filter plate 1, and a nominally transparent part is provided at the other residual part of the cross-shaped plate 1, specially at a center 8. A double acting actuator 7 can sequentially introduce each arm filter to beam that is controlled to pass through the central position 8 of the cross-shaped plate. The filter 1 is not allowed to rotate in the surface.