To simplify the construction work and make a storage shelf with castor and a wheeled chair possible to pass by reducing the height of the whole rail which is provided in a lower part of a folding door and in which a groove in which a wheel runs is formed to mount it on a floor surface and forming a gentle inclination part in a corner part on its both sides.

A lower rail 10 for folding door 18 is made of light metal such as aluminum or iron, stainless steel, etc., and its height H is about 3mm and its width W is about 40mm. Gentle inclination parts 11, 12 having the height A of 2mm and width B of about 5mm are formed on its both sides, and the lower rail 10 for folding door 18 is fixed on a floor surface 13 directly by using a countersunk screw 16, etc. A groove 17 which has a rectangular cross section, the depth D of about 2mm, and the width which is larger than the width of a wheel 20 of a runner 19 attached in a lower part of the holding door 18 by approximately 1 to 2mm is formed at the center of the lower rail 10 for folding door. Consequently, a storage shelf with castor and a wheeled chair can override from parts of the gentle inclination parts 11, 12 and pass.