The objective to be solved by the present invention is to provide an ice-crystallization inhibitor which has a practicable and excellent ice-crystallization inhibiting property and which can be efficiently and stably produced in a safe process suitable for food production. Also, the objective of the present invention is to provide an antibody which specifically reacts with the ice-crystallization inhibitor, and a composition, a food, a biological sample protectant and a cosmetic which contain the ice-crystallization inhibitor. Furthermore, the objective of the present invention is to provide a polysaccharide which is derived from a basidiomycete and which is used for inhibiting ice-crystallization of a liquid containing water, and a method for inhibiting ice-crystallization of a liquid containing water. The ice-crystallization inhibitor according to the present invention is characterized in being a polysaccharide derived from a basidiomycete.