Abstract: A door member such as a garage door is driven by a motor through a roller chain having a finite length to travel in the garage opening and closing directions. The roller chain is driven by a single drive sprocket driven by the motor to make its reciprocating movement along the same path while making rolling engagement at its roller portion with a guide rail constructed to support the roller portion of the roller chain from the opposite sides. A trolley connected to the door member by an arm is releasably coupled to the roller chain and is also guided along the guide rail while making sliding engagement therewith. A mechanism for detecting abutment of the door member with an obstruction present on the traveling path is provided to detect the above situation when a physical force is imparted to the roller chain due to the abutment. The opening and closing movement of the door member, stopping of rotation of the motor and detection of the presence of an obstruction are electrically controlled.