A seat reclining device has a torsion spring for a cam, and a plurality of guide-protrusion pairs formed integral with the inside face of a stationary member for guiding movement of tooth blocks into and out of meshed-engagement with an internal tooth of a movable member. Two opposing circular-arc concave portions are formed on opposing faces of two circumferentially adjacent guide-protrusion sets. A space between the concave portions is dimensioned to be wider on a radially outward side for defining a spring accommodation space, and dimensioned to be narrower on a radially inward side for forming circumferentially-opposing convex portions. Two spring hooks engage with the respective convex portions under preload. One of the hooks is also engaged with the cam for forcing it in its locked direction. An anti-rotation protrusion is formed on the outside face of the stationary member at a position conforming to the spring accommodation space.