Seat belt retractor, seat belt apparatus, and vehicle with a seat belt apparatus

In order to provide a technology effective for miniaturization of a seat belt retractor to be installed in a vehicle, a retractor (130) of a seat belt apparatus is structured such that a driving shaft as the rotational axis of a motor (133), a spool shaft as the rotational axis of a spool (132), and a speed-reduction shaft as the rotational axis of a motor speed-reduction mechanism for reducing the rotational speed of the motor are generally aligned in a straight line along the width direction of the spool outer periphery (132a).