PURPOSE: To facilitate fitting, and also to ensure secure operation by detecting the rotational position of an electric motor, and also by converting this rotational position into the position of an automatic door, so that a stop signal can be formed in a prescribed position of the door.

CONSTITUTION: An motor 2 that is connected to a motor driving part 5 is connected via a belt 4 to an automatic door 3 provided with a hole-sensor 1 for detecting the rotational position of the rotor. And the output signals of the sensor 1 are subjected to counter calculation via an input processor 6, and the motor 2 is connected to a CPU 7 into which the signals of a start information unit 8 and a memory 9 are input. By turning the motor 2, the position of the door 3 is calculated, and making the information of the position of the door 3 obtained by calculation, when the door come to a prescribed position, a stop signal is generated to stop the motor 2, and the door 3 is stopped, and also the acceleration and deceleration of the door 3 is carried out by the stop signal.