An automotive seat safety mechanism includes a seat back and a webbing arranged between the seat back and a vehicle roof. A retractor urges the webbing in a winding direction while simultaneously permitting the webbing to be drawn out in an unwinding direction when in a normal state and prevents the webbing from being drawn out when deceleration of the vehicle becomes greater than a predetermined value. A bypassing mechanism is arranged above the seat back. A pretensioner is included in the retractor. The retractor is arranged above and rearward from the seat back. The webbing extends between an upper position of the seat back and the retractor bypassing the bypassing mechanism. The webbing is disengaged from the bypassing mechanism when forward deceleration becomes greater than a predetermined value. The pretensioner is activated to quickly draw in the webbing in response to the forward deceleration.