Abstract: A three-dimensional structure of a protein is predicted by reproducing turns. An amino-acid-sequence read-in unit reads in an amino-acid sequence as a primary sequence, and a secondary-structure prediction unit predicts secondary structures corresponding to the amino-acid sequence. In a three-dimensional-structure prediction unit, a turn-forming-portion calculation unit calculates the number of amino acids forming the turn based on the predicted secondary structures. In a turn-information DB, information on structures of probable turns is registered, where the information is obtained according to secondary structures and the numbers of amino acids. The turn prediction unit searches for information on a structure of a probable turn, based on the secondary structures and the calculated number of the amino acids, and reproduces the turn based on the information which is searched for.