Seatbelt retractor

The object is to provide a seatbelt retractor in which a locking mechanism can be rapidly operated upon occurrence of an emergency without giving sensation of pressure to a vehicle occupant in a normal state. A reduction gear (13) and sun gear (13b) are integrally rotated by rotation of a motor (8). Thereby, planetary gears (16) rotate on their axes, but because an internal gear (18) rotates freely when a retaining lever (21) is not engaged with the internal gear (18), the planetary gears (16) do not revolve, so that rotation of the motor (8) is not transmitted to a spool. When the retaining lever (21) is engaged with the internal gear (18), the internal gear (18) cannot rotate so that the planetary gears (16) revolve and a carrier gear (14) connected to the planetary gears (16) rotates, so that a rotational force of the motor is transmitted to the spool.