1. A seat belt safety apparatus for a vehicle, the seat belt safety apparatus, comprising:a webbing wound into or drawn out of a retractor to hold a passenger in a seat; and
a pretensioner spaced apart from the retractor and including a plurality of guides around which the webbing is wound and an actuator providing actuating force to the guides,
wherein one of the plurality of guides is configured to move away from another of the plurality of guides to apply a holding force to the passenger by pulling the webbing when the actuator is operated and the guides are moved away from each other, and
wherein the retractor and the pretensioner are installed on a seat frame, the retractor is disposed under the pretensioner, and the webbing extends upward diagonally with respect to the seat frame and is wound around the guides without overlapping.