An armrest includes a stationary shaft, fixed to a seat frame, the shaft is inserted and is rotatable about an armrest body, a spring wound around the shaft, one end of the spring being a stationary-side hook locked to the armrest, the other spring end being a free-side hook, a hook-supporting part supporting the free-side hook in a raised direction of the shaft, a hook-joint enlarging a spring diameter by dropping the free-side hook on the hook-supporting part downward in the axial direction of the shaft, and a cam on the shaft 2 and having an unlocking cam part for unlocking the spring by dropping the free-side hook from the hook-supporting part into the hook-joint when the armrest body is rotated, and a relocking cam part for locking the spring by raising the free-side hook from the hook-joint and supporting it by the hook-supporting part when the armrest body is rotated.