Abstract: An improved armrest adjusting mechanism for use on a vehicle's seat is provided with a slide board housed in an adjusting bracket. The slide board has a dentate portion having a plurality of dents which are in retaining engagement with a pivotal retaining ratchet secured to the adjusting bracket. The adjusting bracket can only be pulled upwardly in adjustment so as to make the armrest extended. The lowering of the armrest can be easily effected by pulling the adjusting bracket all the way up its top end, taking the retaining ratchet out of the moving path of the dentate portion of the slide board with the ratchet retained in place by a locking pole which is brought to the bottom of an elliptic through hole when the adjusting bracket is pulled to its top end. Then, the adjusting bracket is pushed downwardly and the retained locking pole will be pushed out of retaining engagement with the spring biased retaining ratchet and the locking pole moves to the top end of the elliptic through hole.