PURPOSE: To take in/out a cargo easily by protruding the door end part of one side horizontally sliding door body from other one for making easy ordinary opening and closing, aligning the door end parts of both horizontally sliding door bodies as necessary, and enlarging its opening sufficiently.

CONSTITUTION: Plural sliding door bodies 1a, 1b are built in so as to slide side by side in a horizontal direction. A bar-shaped spacer 4 which runs and stops at a position where its door top end part 1a' protrudes from the top end part 1b' of the other sliding door body 1b is mounted so as to change its posture to a standing posture of standing and retracting and a working posture of turning-down in the roughly horizontal direction while prevecting the one side sliding door body 1a from coming in contact with a door contact part 3 is mounted at the door contact part 3 which keeps a door in its opening condition by bringing the door end part of one side sliding door body 1a into contact with it.