Patent ID: 8141808

Claim:
A seat belt device comprising: a spindle for winding a seat belt; a frame for rotatably supporting the spindle, the frame containing magnetic material; a biasing unit for biasing rotation of the spindle in a winding direction of the seat belt, the biasing unit containing magnetic material; a rotation detection unit for detecting rotation of the spindle; and a cover member which accommodates the biasing unit and the rotation detection unit, the cover member is installed on side plates of the frame, wherein the rotation detection unit comprises: a magnetic disc rotating together with the spindle; and N pole and S pole disposed alternately around an outer circumference of the magnetic disc at intervals of a constant pitch in a circumferential direction, wherein the magnetic disc detects a change in a magnetic field due to the rotation of the magnetic disc in accordance with a rotation of the magnetic disc, and the magnetic disc is disposed between the frame and the biasing unit.