PURPOSE: To prevent a guide for the sliding movement of a sliding door relative to a fixed door from appearing on the floor side and to facilitate installation of such a guide.

CONSTITUTION: A sliding door 2 is provided which is opened and closed by sliding relative to a fixed door 1. An upper rail 3 is provided along the sliding range of the sliding door 2. The sliding door 2 is hanged to the upper rail 3 via a slide 7 in such a manner as freely sliding. A small piece of a guide tool 4 for guiding sliding of the sliding door 2 is disposed at the lower end portion of the fixed door 1 which is located on the side of the sliding door 2. When the lower end portion of the fixed door 1 located on the side of the fixed door 1 is fixed to an open fixed frame 5 by means of screws 6 such as bolts, the guide tool 4 is sandwiched between the fixed door 1 and the open fixed frame 5 to fix the guide tool 4.