The present application relates to a technical field of a seat belt retractor that carries out at least one of retracting operation and withdrawing operation for a seat belt by rotating a spool with an electric motor, and a seat belt apparatus provided with the same, and particularly to a technical field of a seat belt retractor where the electric motor is controlled with an electronic control unit (ECU), and the seat belt apparatus using the same. 
Generally, a seat belt apparatus mounted on a motor vehicle such as an automobile or the like is configured to restrain an occupant in the event of an emergency, such as a collision.  Such a seat belt apparatus is provided with a seat belt retractor for retracting the seat belt.  The seat belt is wound on a spool when the seat belt is not in use, and is withdrawn and worn by the occupant when used for protection.  A locking mechanism of the seat belt retractor is activated in the above-described emergency and a rotation of the spool in a seat belt-withdrawing direction is blocked, and thereby prohibiting the withdrawal of the seat belt and thereby, restraining the occupant in the emergency. 
Traditionally, a seat belt apparatus is provided with a seat belt retractor for carrying out retracting operation for a seat belt by controlling the rotation of a spool with an electric motor. 
It is desirable to provide a seat belt retractor capable of protecting an electronic control unit integrally provided in a seat belt retractor from an external force, suppressing noise caused by the electronic control unit, to be affected to any of other electronic parts, and improving assembling workability by compactly forming the seat belt retractor, and a seat belt apparatus using the same.