To mold a prefabricated gate door without using a core form by arranging a front half body and a rear half body back to back, fixing the same to each other, and providing a gate door accessory housing portion.

A front half body 1 and a rear half body 2 are arranged back to back to fix the same to each other, and a gate door accessory housing portion 4 is formed at an abutted portion, in which gate door accessories 5 are housed. A peripheral frame portion 6 is formed at each of the front half body 1 and the rear half body 2, and the gate door accessory housing portion 4 may be formed at the portion 6. Further, a faceplate 7 may be interposed at the abutted portion between the front half body 1 and the rear half body 2. Still further, a faceplate fitting portion 8 for fitting the faceplate 7 may be provided, and a faceplate inserting opening 9 for inserting the faceplate 7 may be sequentially formed at a portion of the faceplate fitting portion 8. Thus, unlike a conventional case where a core form is used or cutting is required as after- working, the gate door accessories can be housed, which leads to improved appearance of the gate door.