Provided is a slide door device for a vehicle, including: a body side lower rail disposed below a door opening formed on a side of a vehicle body and extends in a front-rear direction; a body side rail disposed above the body side lower rail and behind the door opening and extends in the front-rear direction; a door side lower guide roller unit and a door side guide roller unit connected to a slide door and configured to slide on the body side lower rail and the body side rail respectively; a door side lower rail disposed in a lower portion of the slide door positioned below the floor surface in the door opening and extends in the front-rear direction; and a body side lower guide roller unit connected to the lower portion of the door opening and configured to slide on the door side lower rail.