Sliding door apparatus and elevator

In a slide door device, a first doorway is opened and closed by a first door and a second doorway facing the first doorway is opened and closed by a second door. At a side portion of the space between the first doorway and the second doorway, there is placed imaging means for imaging the space side. An image processing and determination section determines, based on image data from the imaging means, whether there is an obstacle in the space.