To enable to stably support a slide door at the rearmost position in a movable range thereof.

The slide door apparatus is provided with a slide door 4 which opens and closes an opening 3 by moving in the front-and-rear direction, an upper rail 5 extending along an upper side of the opening 3, an upper arm 8 whose one end is guided by the upper rail 5 and the other end is fixed to the slide door 4. Furthermore, the apparatus includes a stopper member 38 coming close to the upper arm 8 when the slide door 4 moves to the rearmost position in its movable range as well as two pieces of stopper pins 21 which are formed to project from the upper arm 8 and are received by the stopper member in such a state as the upper arm 8 is brought close to the stopper member 38.