To provide a lift gate door for being opened or closed more smoothly than a conventional lift gate door, preventing the door or the like from crashing against the ground or a stopper or the like when opening or closing it completely without fail, and preventing the occurrence of unpleasant crashing sound and the reduction of its service life due to crashing.

This lift gate door 1 includes an arrival detecting means 14 for detecting arrival of the door 6 moving toward the door completely opened position by turn of arm means 4 and 5 in A direction at the position immediately before door complete opening and arrival of the door 6 moving toward the door completely closed position by turn of the arm means 4 and 5 in B direction at the position immediately before door complete closing, respectively, and a DC voltage control part 15 for supplying DC voltage to a DC electric motor 9 and releasing supply of DC voltage to the DC electric motor 9.