A sliding door device for a vehicle includes a door panel for opening and closing a door opening and covered by an upper trim and a lower trim, and a center rail mounted on the door panel to extend in a longitudinal direction of the vehicle body and providing a path for a center roller mounted on a center portion of the vehicle body, wherein a lower portion of the upper trim and an upper portion of the lower trim are disposed to overlap each other vertically. The center roller is mounted on a center roller mounting bracket including a first surface extending toward the vehicle body to be vertical to the door panel, a second surface bent from the first surface toward a lower side of the vehicle body, and a third surface extending from the second surface toward the vehicle body to be vertical to the door panel.

A slide door support device supports a slide door that opens and closes a door opening formed on a side surface of a vehicle body. The slide door support device includes first and second lower rails and a lower guide unit. The lower guide unit includes a first lower guide roller moving along the first lower rail, a second lower guide roller moving along the second lower rail, a lower fixed portion fixed to the slide door, a lower rotational arm rotatable relative to the lower fixed portion and supporting the first and second lower guide rollers, and a pressing member pressing the lower fixed portion. An arm angle made by the lower fixed portion and the lower rotational arm gradually decreases as an opened degree of the slide door decreases. The pressing member presses the lower fixed portion in a direction of increasing the arm angle.

A sliding door device for a vehicle includes a door panel for opening and closing a door opening and covered by an upper trim and a lower trim, and a center rail mounted on the door panel to extend in a longitudinal direction of the vehicle body and providing a path for a center roller mounted on a center portion of the vehicle body, wherein a lower portion of the upper trim and an upper portion of the lower trim are disposed to overlap each other vertically. The center roller is mounted on a center roller mounting bracket including a first surface extending toward the vehicle body to be vertical to the door panel, a second surface bent from the first surface toward a lower side of the vehicle body, and a third surface extending from the second surface toward the vehicle body to be vertical to the door panel.