PURPOSE: To facilitate the maintenance, service and the like of the automatic open door device.

CONSTITUTION: The device is provided with a mobile door 3 which is moved to the direction indicated by an arrow head X while the upper end of its one side section 3a is being rotatably supported via a hinge section 3b, a wing door 4 where its one side section 4a is rotatably supported via a hinge section 4b, an energizing means energizing a mobile door 3 provided within the one side section 4a of the wing door 4 to the direction indicated by an arrow head R, a guide rail 15, a slide rail 16, a direct actng guide bearing 17, and with an interlock means made up of a wear plate 18, and of a guide roller 20. The mobile door 3 and the wing door 4 are interlocked by the interlock means at the time of rotational operations. When operation, maintenance and the like are carried out, complicated operations that the rotating speeds of the mobile door 3 and the wing door 4 have to be independently adjusted, can thereby be eliminated.