Abstract: The armrest of the present invention includes a first horizontal plate provided horizontally with a tabletop, a second horizontal plate jointed to the first horizontal plate by way of a hinge, this second horizontal plate forming a continuous horizontal surface along with the first horizontal plate when the hinge is opened, and the second horizontal plate being folded on the first horizontal plate so that a surface of the second horizontal plate meets a surface of the first horizontal plate when the hinge is closed, and a vertical plate provided vertically to the rear surface of the second horizontal plate. When the person sets a position in which he/she holds both arms down on the sides of the body, the hinge is opened, thus forming one horizontal plane, on which both arms can be laid down. When the person sets a position in which he/she folds both arms across the head, the hinge is closed, and the surface of the second horizontal plate is folded on the surface of the first horizontal plate.