level voltage signal that is sent to the related input terminal of the control portion 100 hereinafter called the microprocessor during s12 this signal is interpreted by the microprocessor as an opening closing demand if the door opening closing demand exists at step s12 the program proceeds to step s14 where the microprocessor 100 determines whether or not door opening closing is presently occurring if door opening closing is in operation at step s14 the program proceeds to step s16 where the micro processor 100 ignores the door opening closing demand if door opening closing is not in operation at step s14 the program proceeds to step s18 where the microprocessor 100 determines whether both the contact points of the reed switch 28 hereinafter called an open sensor and the reed switch 65 hereinafter called a closed sensor are closed 34 on 34 state or not in the case where both the open sensor 28 and closed sensor 65 are on the related input terminals of the micro processor 100 are receiving low level voltages and step s18 returns a 34 yes 34 value this situation case 4 fig6 occurs when there is a sensor malfunction and the program proceeds to step s20 where an error sound is issued and the door motor 31 is not driven if at least one of the sensors 28 65 is off during step s18 the program proceeds to step s22 where the microprocessor 100 determines whether both the open sensor 28 and closed sensor 65 are off the case where both the open.