To provide an interlocking opening/closing device for double sliding doors different in width, and to provide a fire door.

The interlocking opening/closing device is constructed by arranging pulleys 5, 5 at locations that are above the respective sliding doors when fully opened, endlessly straining a wire rope 7 having a cylindrical guide 6 fitted thereon, between both the pulleys, once returning the double sliding doors to a fully closed position, thereafter fixing a wire rope fixture 8 overhanging from the narrow-width door to the wire rope on a side without the cylindrical guide, and then connecting a fixture 9 overhanging from the wide-width door to the cylindrical guide. Then a first fastener 10 of the cylindrical guide is fixed to the wire rope on a side with the cylindrical guide at a location P at which the cylindrical guide cannot move toward the narrow-width door from the door fully closed position, and a second fastener is fixed to a location Q separated from the first fastener fixed location toward the cylindrical guide by a distance equal to a difference between widths of both the sliding doors and the length of the cylindrical guide, to thereby carry out opening/closing operation of the wide-width sliding door.