To improve workability in assembling an armrest and to mount an outer covering member onto an armrest body in various kinds of configurations.

This armrest 20 is equipped with an armrest body 30 placed upright at the side of a seat and an outer covering board 40 mounted on the upper surface of the armrest body 30. A certain number of inserting pins 51 are placed vertically on the upper surface of the armrest body 30, and a three- steps hole 41 opposing to each inserting pin 51 is formed on the bottom surface of the outer covering board 40. A push nut 52 which allows the movements of the inserting pin 51 in an inserting direction and interrupts the movements of the inserting pin 51 in a direction opposite to the inserting direction is mounted in the three-steps hole 41.