To provide gate door fixing structure in which manufacture and execution are simple and a gate door is fixed in a closed state by disposing a slide rod fitted in a gate side rod receiving part on the gate door openably supported on a gatepost and capable of stopping at an arbitrary position.

Two parallel doors are supported with right and left gateposts 2 by a hinge hook and eye 2, and opened and closed in both of forward and backward directions, any one of them by operating a knob 4. A lateral slide rod 5 is disposed on respective lower ends in the door, and a rod receiving part fitting in the end of the lateral slide rod 5 is provided on the downward hinge hook and eye. A thread ridge is provided on the knob part 6, and the lateral slide rod 5 can be stopped at an arbitrary position. The hinge hook and eye is arranged on a gatepost 3. Thereby the lateral slide rod 5a of one door 1a is slid to the side of the gatepost 3a to fix the door 1a, and only a door 1b can be freely opened and closed. Thus, the gate door can be surely fixed, and gate door fixing structure easy in manufacture and execution can be obtained.