VEHICLE SEAT RECLINING DEVICE

In this vehicle seat reclining device, the annular protrusion of a ratchet has a first region, a second region, and a third region, which are arranged circumferentially, and the outer side surface of the ratchet has a fourth region. The protrusion is shaped so that the third region extends further radially outward than the second region. As a result, the portion of the fourth region, which corresponds to the third region, extends further radially outward than the portion of the fourth region, which corresponds to the second region.