PURPOSE: To exhibit a high function with a simple structure and to enhance the safety by using a d.c. linear motor as a drive source, and by reversely exciting an armature coil when a door is moved at a speed higher than a predetermined speed.

CONSTITUTION: An armature 32 of a multi-phase brushless d.c. linear motor 1 uses as a door drive source is mechanically coupled to a door which is therefore directly driven. Further, the position and speed of the door is always detected in accordance with signals form magnetic sensors 3a through 3c for driving on the armature 32 or a stator. When the door is moved at a speed exceeding a predetermined speed, the armature coils 2a through 2c are reversely excited so as to control the speed of the door in order to maintain the speed below the predetermined speed. With this arrangement, it is possible to avoid danger such that the door impinges against the opening or closing end, or that a human is caught.