To provide a horizontally sliding movable weir which can reduce the space for housing a door body and can secure sufficient strength of the door body.

The horizontally sliding movable weir 1 comprises the door body 10 with horizontal flexibility which can close an opening part by overlapping an outer peripheral edge of the opening part, two vertically extending shaft members 20, 30 arranged on both lateral sides of the opening part, respectively, and two ring-like chains 40, 40 fitted to the shaft members 20, 30 in a bridging manner. The upper end edge and the lower end edge of the door body 10 are connected to the chains 40, 40, respectively. When the chains 40, 40 are rotated and the door body 10 is moved horizontally, the door body 10 is folded back around the shaft members 20 along the chain line of the chains 40, 40.