A filter element includes a first glass substrate having a pair of parallel surfaces and a band pass filter arranged on one of the parallel surfaces, a pair of single-crystal substrates (Si wafers) each including a primary surface formed with a depression having an inclined surface with respect to the primary surface occupying at least one half of the opening of the depression, and a second glass substrate having an optical element. The primary surfaces of the single-crystal substrate pair are bonded to a pair of the surfaces of the glass substrate. The depressions are faced through the glass substrate and surround the band pass filter. By this configuration, the filter element can be mass produced with a high accuracy and a low cost by the wafer-level process.