An assist device includes a first body-worn unit that is worn on at least shoulders or a chest of a user; a second body-worn unit that is worn on each of right and left legs or a waist of the user; a belt body provided to extend along a back side of the user, from the first body-worn unit to the second body-worn unit; an actuator provided in the first body-worn unit or the second body-worn unit and allows a part of the belt body to be reeled and unreeled; a battery configured to supply electricity to the actuator; and a controller configured to control the actuator. When a remaining charge level of the battery has decreased to a predetermined set value, the controller executes a vibrating motion process of causing the actuator to perform a vibrating motion of intermittently repeating reeling of a minute amount of the belt body.