Acceleration sensor and seat belt retractor

There is provided an acceleration sensor enabling precise positioning of a sensor lever of the acceleration sensor, for ensuring a stable operation of the acceleration sensor, and a seat belt retractor including the acceleration sensor. Shafts of a sensor lever projects from a base. The sensor lever is supported between supports of a sensor holder so as to be rotatable and shiftable in a rotation axis direction. The sensor lever is rotated by displacement of an inertia mass. A limiting portion of the sensor holder is brought into contact with contact portions of the sensor lever. The limiting portion limits shifting of the sensor lever in the rotation axis direction, so as to avoid contact between the base and the supports.