Recliner adjuster

A recliner adjuster for appropriately adjusting an inclination of a seat back with respect to a seat cushion includes a worm rotatably mounted on the seat cushion, and a helical gear held in engagement with the worm and mounted on the seat back via an auxiliary locking mechanism. The auxiliary locking mechanism includes a pair of external gears connected to the helical gear and held in engagement with a portion of the seat back, and a pair of internal teeth mounted on the seat cushion so as to accommodate the pair of external gears therein, respectively. During normal use, the seat back is held at a predetermined angle with respect to the seat cushion by the engagement of the helical gear with the worm, while when a load greater than a predetermined value is inputted to the seat back, the pair of external gears are partly deformed to engage with the pair of internal teeth, respectively, to thereby hold the seat back at the predetermined angle with respect to the seat cushion.