To provide a seat belt device capable of securing the safety of an occupant by adjusting the tension of a seat belt in accordance with the physique and the weight of the occupant and capable of preventing the occupant from feeling a sense of discomfort when the seat belt is wound up.

This seat belt device 1 is provided with a collision prediction device 4 for detecting the collision of a vehicle beforehand, an occupant detection device 3 capable of determining the state of the occupant on a seat, the seat belt 7 for restricting the occupant on the seat, a seat belt drive device 6 for winding up and pulling out the seat belt 7, and a seat belt control device 5 for driving the seat belt drive device 6 based on a signal from the collision prediction device 4 and occupant information from the occupant detection device 3 and winding up the seat belt 7 in order to have tension in accordance with the occupant.