To provide an arm rest device capable of evacuating the arm rest without a sense of incompatibility as much as possible.

The movement of an arm rest without being intended is found not to occur by evacuating the arm rest on the basis of getting-off will of an occupant. The arm rest device includes: the arm rest 10 provided in the outside of a vehicle width direction of seats (21-23) mounted on a vehicle; a drive part 111 for moving the arm rest 10 between a storing position and a developing position; a getting-off will detection part for detecting the getting-off will of the occupant; and a control part for controlling the drive part 111 so that the occupant evacuates the arm rest 10 at a position where the occupant can separate from the seats (21-23) without any obstacle in response to getting-off will detection of the getting-off will detection part.