The object aims to form and maintain a cell, a tissue or an organ induced by differentiation. Disclosed is a composition for inducing the differentiation of a cell capable of being differentiated in a given direction to thereby produce a cell, a tissue or an organ through the further induction of the differentiation in the given direction. The composition comprises NELL-1 or a substance which can be altered so as to act as NELL-1 upon the differentiation. Also disclosed is a composition for maintaining a cell, a tissue or an organ produced by the induction of the differentiation.
