A seat belt device in an automotive seat, which comprises a seat belt extending from a part of the automobile to a floor of the same for restraining a passenger to the seat, and a seat belt guide provided at one upper corner portion of the seat back of the seat.The seat belt guide includes a guide anchor through which the seat belt slidably passes, and a drive mechanism for causing such through guide anchor to be moved in a vertical direction along the longitudinal direction of the seat back. Thus, the initial point at which the seat belt begins to approach a passenger may be set at a desired level via the guide anchor, thereby adapting the seat belt to better fit, and hence better restrain the passenger's trunk to the seat, irrespective of his or her individual physical differences and/or inclination of the seat back.