To close an automobile door provided for an automobile main body by small force.

When a rear door 12 is closed to a predetermined half-closed condition, a tip part of an engaging arm 18 comes into contact with a hook 17, and furthermore, the tip part of the engaging arm 18 comes off from the hook 17 and rides on the hook 17 so that preliminary catching is completed. Furthermore, a motor of a drive source 19 is rotated, a shaft is elongated, the hook 17 is pushed downward by the engaging arm 18, and the rear door 12 is closed.