Two methods of the in-situ observations of ice crystal growth from the supercooled water including impurity are briefly summarized. The free growth method of crystal is very useful to observe the growth as a function of the driving force for crystal growth (namely, supercooling temperature). The one-directional growth method is often used to observe the morphological instability and the pattern formation. As a typical example of the in-situ observation, the pattern formation at the interface between ice and KC1-solution is analyzed by the way of Mach-Zehnder interferometer. The mechanism of the morphological instability is discussed as the effect of impurity included in the water.
