A seat-belt retractor comprising a seat-belt spindle which is rotatably mounted in a housing, an electric motor for driving the seat-belt spindle, and a gear mechanism that transmits the rotational motion from the electric motor to the seat-belt spindle, wherein: the gear mechanism, when deactivated, can be driven as an assembly for driving the seat-belt spindle with a first torque; the seat-belt retractor has a first part, which, when a tensile force exerted by the seat-belt is exceeded, is driven in a rotational motion opposite to that of the rotational direction of the electric motor; and a braking device, which brakes the rotational motion of the first part, thereby actuating a blocking device blocking a second part of the gear mechanism, the blocking device activating the gear mechanism to transmit the rotational motion of the electric motor in a reduction ratio to the seat-belt spindle.