PURPOSE: To require not so much of maintenance work, etc., and, at the same time, to prevent the burden of force on hands, etc., suddenly when a sliding door is opened and closed or the stiffness of opening and closing operation.

CONSTITUTION: A first door 3 on the door front side and a second door 4 on the door base side are connected to each other through an air damper 15 as a buffer, and the doors 3 and 4 can be smoothly opened and closed by transferring movement operation of the first door 3 to the second door 4 while buffering it to move the second door 4, accordingly, the burden on hands suddenly when the doors are opened and closed or the stiffness of opening and closing operation can be prevented. By using the air damper 15 as the buffer, execution can be simply carried out and, at the same time because there is no component such as wire, etc., maintenance work, etc., are rarely required.