A rotatable armrest includes: a housing; a button system; and a hinge system engaged to the button system, in which the button system and the hinge system are provided in the housing, in which the hinge system includes a hinge shaft, and the rotatable armrest is fixed at a first position, a second position, or a third position by being rotated about the hinge shaft, and in which the rotatable armrest is configured to be positioned to be folded downward at the first position, the rotatable armrest is configured to be positioned to be directed forward horizontally at the second position, and the rotatable armrest is configured to be positioned to be directed rearward horizontally at the third position.