To provide a trap gate door capable of reducing the electric power necessary for opening/closing motion of the door by the motion of an electric motor and stably opening/closing the door.

The trap gate door 1 is provided with arm means 81, 82 where the gate door is supported by supports 2, 3 at one end and the door 13 is fitted to the other end, an automatic arm rotation means 29 of the arm means 81, a control means 34 controlling the rotation of the arm means 81, and an electromagnetic brake 58 prohibiting the A and B directional rotation of the arm means 81 based on the electromagnetic force supplied/nonsupplied to the electric motor 36 of the automatic arm rotation means 29 on one hand, releasing the prohibition of the A and B directional rotation of the arm means 81 based on the electromagnetic force, while the electric supply to the electric motor 36 of the automatic rotation means 29 is stopped, on the other hand.

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