  We investigated the central gas systems of E/S0 galaxies by making use of the
WFPC2 images of the Hubble Space Telescope archive. We searched the gas systems
that were traced by the dust with a new method of making color excess images in
F555W - F814W (V-I). Out of 25 sample galaxies, we detected gas system in 14
galaxies. The dust was newly detected in two galaxies that were thought to
contain no dust based on single band, pre-refurbishment data. The full extents
of the gas systems are 0.1 to 3.5 kpc, and the masses of the gas, log M(gas)
[M(solar)], are 4.2 to 7.2. The AGN activity is well correlated with existence
of the gas systems. None of galaxies without the gas systems show the AGN
activity. On the other hand, some galaxies with the gas systems show the AGN
activity; optical AGN activities are shown in 5 out of 11 galaxies of which
AGNs are optically studied, and radio activities are shown in 6 out of 14
galaxies. This shows that the AGN activity is driven with the gas system.
