In general, an automatic door opening and shutting device detects either person(s) or vehicle(s) coming in and out the door by a detecting means using a limit switch or a photoelectric tube. And by actuating an opening and shutting means with detecting signals, the door is opened or shut automatically. In case the automatic door is opened or shut by a friction drive system, the disadvantage is that power transmission on the friction surface tends to become irregular due to some shakes of the door being caused during the door opening or shutting, and then the automatic door is not actuated smoothly.
Further, in case the automatic door is switched to a manual operation by some accidents and other causes, it is forced to be opened or shut with a stronger force because a load of a friction drive means is applied to the friction surface of the door. Accordingly, it is not easy to open or shut smoothly by hand the door which ceased its automatic function.
For the sake of removing the aforegoing defects and disadvantages, the present invention has been achieved.