An opening/closing door unit and an immobile part, said door unit for disposal in an opening of a doorway in use, the opening having a lateral width, the immobile part being a frame member in which the opening/closing door unit is installed, said door unit comprising: a door body; a movement support part comprising an axial part 41a for turnably hanging the door body at a door-end side, a supporting bracket 41b fixed to the upper side of the axial part 41a, hangers 41c turnably supported by the supporting bracket 41b, and a guide rail for guiding the movement support part in a lateral width direction of the opening relative to the immobile part in use; the door body supported by the movement support part in such a manner so that the door body is moved in the lateral width direction of the opening while being turned in an axial direction to intersect the opening, with the opening opened and closed by the movement and the turn of the door body, and wherein the door unit further comprises a linear motor for moving the movement support part in the lateral width direction of the opening along the guide rail in use, said linear motor including a stator located in the immobile part and a movable element provided in the movement support part; and furthermore comprising a magnetic attractor for holding the door body closed; characterised in that the magnetic attractor is fixed to the immobile part, on a door-end direction side from the movement support part when the door body is almost fully-closed, and the movement support part is attracted to said magnetic attractor, and wherein a gap is provided between the magnetic attractor and the supporting bracket when the door body is fully-closed, so that an attraction force of the magnetic attractor can act, and that no part of the magnetic attractor contacts the movement support part when the door body is fully-closed. a door body; a movement support part comprising an axial part 41a for turnably hanging the door body at a door-end side, a supporting bracket 41b fixed to the upper side of the axial part 41a, hangers 41c turnably supported by the supporting bracket 41b, and a guide rail for guiding the movement support part in a lateral width direction of the opening relative to the immobile part in use; the door body supported by the movement support part in such a manner so that the door body is moved in the lateral width direction of the opening while being turned in an axial direction to intersect the opening, with the opening opened and closed by the movement and the turn of the door body, and wherein the door unit further comprises a linear motor for moving the movement support part in the lateral width direction of the opening along the guide rail in use, said linear motor including a stator located in the immobile part and a movable element provided in the movement support part; and furthermore comprising a magnetic attractor for holding the door body closed; characterised in that the magnetic attractor is fixed to the immobile part, on a door-end direction side from the movement support part when the door body is almost fully-closed, and the movement support part is attracted to said magnetic attractor, and wherein a gap is provided between the magnetic attractor and the supporting bracket when the door body is fully-closed, so that an attraction force of the magnetic attractor can act, and that no part of the magnetic attractor contacts the movement support part when the door body is fully-closed.