PURPOSE: To automatically close an opened door left as it is so as to dissolve the troublesome closing operation by a passenger, and provide a flag hinge of which the construction is simple and the manufacturing cost is cheap without spoiling the appearance of the door.

CONSTITUTION: This door naturally closing flag hinge is provided with a first connecting plate 12 to be fixed on the door side and a second connecting plate 14 to be fixed on the support side. An operating helical part 20 having a descending helical part 18 on the lower part while forming a shaft hole is fixed to the first connecting plate, and a stationary helical part 24 having an ascending helical part 22 on the upper part while forming a shaft hole is fixed to the second connecting plate, the descending helical part and the ascending helical part are assembled so as to closely slidably fit to each other at one part or the whole part, and a shaft body 26 is insertedly fitted into the shaft hole of the operating helical part and the shaft hole of the stationary helical part so as to constitute the device. When the door is opened and left as it is, the descending helical part is automatically rotationally moved along the ascending helical part by the load of the door so as to close the door.