An armrest device including a stationary shaft 2, fixed to a seat frame, an armrest body 7 in which the stationary shaft 2 is inserted and which is rotatable, a lock spring 3 made of a coil spring tightly wound around the stationary shaft 2, with one end of the coil spring serving as a stationary-side hook 3a locked to the armrest body 7, and the other end of the coil spring serving as a free-side hook 3b A hook-supporting part 12 that supports the free-side hook 3b such that the free-side hook 3b is raised in the axial direction of the stationary shaft 2, a hook-fitting part 13 that enlarges the diameter of the lock spring 3 by dropping the free-side hook 3b on the hook-supporting part 12 downward in the axial direction of the stationary shaft 2, a plate 11 for a hook, where the plate 11 projects from the armrest body 7, and a cam member 5 on the stationary shaft 2. The cam member 5 having (1) an unlocking cam part 5b for unlocking the lock spring 3 by dropping the free-side hook 3b from the hook-supporting part 12 into the hook-fitting part 13 when the armrest body 7 is rotated in the armrest-accommodating direction, and (2) a relocking cam part 5c for locking the lock spring 3 by raising the free-side hook 3b from the hook-fitting part 13 and supporting it by the hook-supporting part 12 when the armrest body 7 is rotated in the armrest-use direction.