A sliding door device for a vehicle includes a front door and/or a rear door. A central rail is mounted on the front door and/or the rear door. A central slider is coupled to the central rail. A lower rail is mounted on a lower side of the vehicle. A lower slider is coupled to the lower rail to move along the lower rail. A central support structure has one end connected to the central slider and another end mounted on the vehicle to support the sliding movement of the central slider. A lower support structure has one end coupled to the lower slider and another end connected to a lower portion of the front door and/or the rear door to support the lower portion of the front door and/or the rear door. A hook locks and releases the central support structure to and from the central rail.