An automatic closing door hinge, an automatic closing door mechanism, and a hinge of the automatic closing door mechanism, for smoothly opening a door or closing, with damping, a door. For example, an automatic door closing mechanism has a hinge having a pair of wing plates one of which has a cylinder in a circular cylindrical form received therein a piston, the other wing plate fixing an upper portion of an operation rod engaged with the piston, the piston being to be advanced and retracted through the operation rod associatively with a rotation of the other wing plate. The automatic closing door mechanism comprises a cam formed on the piston. An engaging part provided in the operation rod and movable in the cam. The cam and the engaging part engaging between the piston and the operation rod. A sphere arranged in a recess formed in an outer surface of the piston. A recess groove formed lengthwise in the cylinder. The sphere rolls along the recess groove, to allow the piston to slide within the cylinder. Impact upon door closing is to be damped by an action of air cushioning within the cylinder due to a return movement of the piston.