The purpose of this study is to measure torsion angle of the human forearm during working and to construct a model for representing the torsion and the difference of the range due to the locations of the arm. The torsion angles of the forearm were measured using Shape Tapes when the subject turned a knob with gripping as much as possible. The difference of the torsion range was examined among the thirty-four knobs, which were placed at the mutually different locations around the subject. It was found that the torsion angle varied with the locations and the point existed where the torsion angle became largest between the wrist and the elbow. Finally a forearm model composed of the ulna and the radius was constructed to represent the torsion and the restriction due to the locations of the arm.