To provide a sliding door which can fully close an opening in a partially-notched rectangular shape.

A part of an outside door 3 of the sliding door 1 is provided with a slit 11, and a retractable inside door 5 into the slit 11 is provided. A guide groove 21, which is provided in the inside door 5, is engaged with a guide 25 which is provided inside the slit 11 of the outside door 3, so that the inside and outside doors 5 and 3 can be connected together. The inside and outside doors 5 and 3 are suspended from a rail 7 which is fixed to a ceiling 17 by means of sash hangers 15 and 9 fixed to upper end surfaces 16 and 8, respectively. When the opening 55 is opened/closed, the outside door 3 is moved in the state of being supported on the rail 7 and the inside door 5, by means of the sash hanger 9, the guide groove 21 and the guide 25, so as to protrude from/recede into a door case 63. The inside door 5 is moved in the state of being supported on the rail 7 by means of the sash roller 15, so as to protrude from/recede into the slit 11 of the outside door 3.