PURPOSE:To improve the energency responce by providing a fastening spring independently from a winding spring for energizing the winding shaft of seat belt in the winding direction of seat belt while providing a clutch mechanism for transmitting the force of fastening spring to the winding shaft. CONSTITUTION:A rotary shaft 3 is arranged coaxially with a winding shaft 1c to be energized continuously in the winding direction by a winding spring 15 and supported rotatably by a cover 12 and a guide 4 fixed to the end section integral with the frame 1a and made engagable/disengagable with the winding shaft 1c through a clutch mechanism 30. One end of fastening spring 11 is stopped to said rotary shaft 3 to fasten the seat belt 1b upon emergency. A coupling member 6 to be energized outward through a sprindboard 7 is contained in the opening 3b and recess 5a formed respectively in the flange section 3a of rotary shaft 3 surrounding a clutch gear 2 on the winding shaft 1c and the innercircumference of a rotatable guide ring 5 covering said flange section 3a to enable engagement with the clutch gear 2.
