To decrease the excess area or length of a gate door body, to lighten the gate door body and to reduce force required for opening and closing.

The lower frame 14 of a gate door body 12 having width slightly larger than a gate passage is extended to one side in the longitudinal direction of the gate door body from an upper frame, and a pair of U-shaped guide grooves 14c having a pair of upper-lower guide walls 14a, 14b continued in the coverall length of the lower frame in the lower frame and being opened to one side in the thickness direction of the lower frame are formed at the thickness direction of the lower frame, thus constituting a lower-frame rail. Guide rollers 5, (5A) installed to supporters 4, 4A disposed in upright on a ground surface in a section nearest to a support 1 erected on one side of the gate passage and on the reverse side to the gate passage of the support are fitted into each guide groove 14c of the lower-frame rail in a rollable manner, and the upper frame of the gate door body is held by the guide rollers in a front and a rear droopingly provided at the upper end section of the support.