Patent ID: 8083262

Claim:
A seat belt retractor for retracting a seatbelt, comprising: a cylindrical member rotatable for winding up the seat belt; a shaft member arranged inside the cylindrical member and being torsionally deformable, said shaft member having one end side in an axial direction connected to said cylindrical member so as to rotate together with said cylindrical member; a plate mounting member arranged in the cylindrical member at an axial end thereof and disposed on an outer periphery of said shaft member at the other end portion in the axial direction so as to rotate together with the shaft member; a locking mechanism for preventing a rotation of the plate mounting member in the seat belt withdrawing direction; and a plate member having one end portion fixed to an outer periphery of said plate mounting member and the other end portion engaging an inner periphery of said cylindrical member, the plate member being plastically deformable so that said plate member is wound onto the outer periphery of said plate mounting member during a relative rotation between said cylindrical member and said shaft member, wherein said plate mounting member includes a first reducing radius portion having a radius gradually decreasing toward a downstream in a winding direction of the plate member onto said plate mounting member, and a second reducing radius portion located on the downstream side relative to said first reducing radius portion and having a radius reducing rate greater than that of the first reducing radius portion.