An optical filter module of the present invention has a flat substrate, an optical
path formed on the flat substrate; a filter insertion groove provided, crossing
the optical path, on the flat substrate; a multilayer filter inserted, dividing
the optical path, into the filter insertion groove; and a pair of covers disposed
on the flat substrate so as to sandwich the multilayer filter. The present invention
enables the omission of the process of adjustment of the optical axis, thus achieving
high operability. At the same time, the present invention ensures fixing and mounting
of the multilayer filter even if the multilayer filter is warped.