  We report the detection of a 9.7 $\mu$m silicate dust absorption feature
toward the Cygnus A nucleus. Its optical depth is, however, significantly
smaller than that expected from the dust extinction toward the background
$L$-band emission region ($A_{\rm V}$ $\sim$ 150 mag). We argue that the most
likely explanation for the small optical depth is that the obscuring dust
exists so close to the central engine that a temperature gradient occurs. Our
calculation confirms that the small optical depth and the spectral energy
distribution at 3--30 $\mu$m can be quantitatively reproduced by this
explanation. Combining this picture with the huge AGN luminosity, the emission
properties of Cygnus A are consistent with those of a type 2 quasar, that is, a
highly luminous AGN that is highly obscured ($A_{\rm V}$ $>$ 50 mag) by a dusty
torus with an inner radius of $<$10 pc, and not by $>$ a few 100 pc scale dust
in the host galaxy.
