An armrest serves as an elbow rest of a seat device in a case where the armrest is tilted forward and serves as a backrest of the seat device in a case where the armrest is raised rearward. The armrest includes an armrest pad configured to elastically support a load applied to a backrest surface forming a part of a front surface of the seat device in a case where the armrest serves as the backrest, an armrest cover configured to cover the armrest pad, a protrusion that protrudes from the backrest surface of the armrest cover and abuts against an upper surface of a seat cushion of the seat device in a case where the armrest is tilted forward, and a cutout portion formed in a region that overlaps the protrusion of the armrest cover in a thickness direction of the armrest.