A belt guide anchor is provided to improve handling operability of a seat belt even when a belt opening angle between a portion of the seat belt adjacent to a retractor and that adjacent to an occupant is increased. A belt guide anchor has a belt insertion hole into which a seat belt is fitted so as to be slidable and expanded portions formed on surfaces of the belt guide anchor facing the interior and exterior, respectively, of the vehicle adjacent to the belt insertion hole. In one form, a thin portion is formed in the expanded portion on the surface facing the interior of the vehicle at a position adjoining a part of the belt insertion hole facing the front side of the vehicle, and a thin part is formed in the expanded portion on the surface facing the exterior of the vehicle at a position adjoining a part of the belt insertion hole facing the rear side of the vehicle. With this, even when a belt opening angle θ is large, the seat belt comes into light contact with the thin portions in the expanded portions. Thus, the friction during drawing of the seat belt is small, and the seat belt can be smoothly drawn out.