To provide an automatic door opening/closing device enabling the easy adjustment of the tension of a wire and the easy correction of the displacement of the fully opened position of a door in adjusting the tension.

This opening/closing device 1 fixes one end part 22a of the wire 22 to a first connection bracket 18, and locks a tension adjusting bolt 27 fixed to the other end part 22b by a lock nut 28 by inserting into an erected piece 18a formed on the first connection bracket 18 to facilitate the adjustment of the tension of the wire 22. Also, since the first connection bracket 18 is mounted on a movable element so as to be positionally adjusted, the displacement of the fully opened position of the door in adjusting the tension of the wire 22 can be easily corrected.