Thermo‐optic effects have been studied with changing temperature of a part of the liquid crystal in a cell. The light transmission through the liquid crystal is subject to hysteresis. The experiments show that the mesophase barely coexists with the solid phase, and that there are transparent, semitransparent, and opaque states in the solid phase. Two new information display devices have been made in experiments on the basis of the display characteristics of the liquid crystal and the hysteresis phenomena in the thermo‐optic effects. The display device in which the mesophase and opaque solid phase are used shows three functions: memory of entry information; variations of the memory state corresponding to a linear analogue value; and temporary erasure of information. The display device in which the transparent and opaque solid phases are used shows such functions that entry and permanent erasure can be done alternately, and that linear analogue information can be stored.