  We discuss how we obtain the spatial distribution of ice on the surface of
the circumstellar disk around young stars. Ice in the disks plays a very
important role in various issues, for instance, on the disk structure, on the
planet formation, on the isotopic anomaly in meteorites, and on the origin of
the sea on the Earth. Therefore, the spatially resolved observation of the
condensation/sublimation front of ice, so-called ``snow line'' is strongly
required. Here, we propose a new method for obtaining the spatially resolved
``snow line'' on the circumstellar disks by observing 3 \micron H$_2$O ice
feature in the scattered light. Based on radiative transfer considerations, we
show that the feature is clearly imprinted in the spectrum of the scattered
light from both optically thick and thin circumstellar disks. We also show that
the scattered light and the H$_2$O ice feature from protoplanetary disks are
detectable and spatially resolvable with the current instruments through a
$H_2O$ narrowband filter around 3 \micron. Finally, we present a diagnostics of
disk dust properties on the $K-H_2O$ and $K-L'$ two color diagram.
