Provided is a torsion bar support structure of a seat belt retractor capable of smoothly rotating a rotary torsion bar and preventing deformation of the torsion bar due to moment applied to the torsion bar by coupling support members to both ends of the torsion bar. The torsion bar support structure of a seat belt retractor includes a housing constituting a main body of the seat belt retractor, a guide drum rotatably coupled to the housing, a torsion bar inserted into the guide drum, a base member fixed to one side of the housing, a locking member fixed to the other side of the housing, and a cylinder accommodating a piston therein to rotate a gear member fixed to the base member, the structure including: a bearing member coupled to the gear member, and a cap surrounding a cover fixing shaft projecting from the locking member, wherein the bearing member and the cap rotatably support the torsion bar when rotation moment is applied in a circumferential direction and an axial direction of the torsion bar.Since a torsion bar is rotatably supported by a bearing member and a cap, the torsion bar can be smoothly rotated by moment applied in an axial direction thereof. In addition, even though axial moment is applied, it is possible to prevent position variation and deformation of the torsion bar. Further, contact resistance between a connector and a projection can be reduced when the torsion bar is rotated, and thus the torsion bar can be smoothly rotated.