To provide a sliding door made of aluminum with which a gap between the door and the inner surface of a lintel rail can be optionally adjusted.

An oscillation preventing fixture 1 is composed of a base body 10 including an attaching piece 11 for a room side paper sliding door, a pair of oscillation preventing pieces 12A, 12B provided in the base body 10 so as to be opposed to each other in the direction orthogonal to a lintel rail, and an extension and contraction adjusting bolt 13 located between the pair of oscillation preventing pieces 12A, 12B and having a thread part engaged in the base body 10. The head part of the bolt 13 abuts against opposed surface walls of the pair of oscillation preventing pieces 12A, 12B, the pair of the vibration preventing pieces 12A, 12B are expandable and contractible in the direction orthogonal to the lintel rail in association with the bolt 13 threadedly moved back and forth.