A door hinge assembly comprising: a hinge shaft; a movable leaf comprising a first portion, pivotably connected to the hinge shaft, and a second portion, connectable to a door, a rotation of the moveable leaf allowing the door to be set in an opened position and in a closed position; and a stationary leaf comprising a first portion, connected to the hinge shaft, and a second portion, fixable to a door frame provided on a wall of an inner space that is opened and closed by the door, wherein a top surface of the movable leaf comprises a base surface and a step-down surface, wherein a height of the step-down surface is lower than a height of the base surface, in the longitudinal direction of the hinge shaft, and the hinge shaft comprises a protrusion on an outer circumferential surface thereof over the top surface of the movable leaf, the protrusion protrudes by a distance to allow the protrusion to be placed on the top surface of the movable leaf, such that, when the moveable leaf is rotated to set the door in the closed position, the protrusion is placed on the base surface, and, when the moveable leaf is rotated to set the door in the opened position, the protrusion is placed above the step-down surface, wherein, when the door is opened, the base surface slides under the protrusion while the movable leaf rotates along with the door, and then the protrusion descends toward the step-down surface by gravity to be located above the step-down surface, in a position lower than the base surface, the top surface of the movable leaf further comprises a vertical surface defined between the base surface and the step-down surface, and a rotation of the movable leaf in a closing direction of the door is blocked by the protrusion located upstream of the vertical surface with respect to the closing direction of the door, so that the door remains in the opened position, characterized in that the door hinge assembly further comprises a stopper unit disposed between the stationary leaf and the hinge shaft and arranged to control a distance by which the protrusion descends towards the step-down surface, wherein the stopper unit comprises a step extending from a wall surface of the stationary leaf facing the hinge shaft and a protrusion protruding from the outer circumferential surface of the hinge shaft, the protrusion of the stopper unit being allowed to be placed on the step of the stopper unit, when the door is set in the opened position, and wherein a distance between the step and the protrusion of the stopper unit is smaller than the difference in height between the base surface and the step-down surface of the movable leaf, or smaller than a distance between the protrusion of the hinge shaft and the step-down surface of the movable leaf, as seen when the door is set in the closed position. a hinge shaft; a movable leaf comprising a first portion, pivotably connected to the hinge shaft, and a second portion, connectable to a door, a rotation of the moveable leaf allowing the door to be set in an opened position and in a closed position; and a stationary leaf comprising a first portion, connected to the hinge shaft, and a second portion, fixable to a door frame provided on a wall of an inner space that is opened and closed by the door, wherein a top surface of the movable leaf comprises a base surface and a step-down surface, wherein a height of the step-down surface is lower than a height of the base surface, in the longitudinal direction of the hinge shaft, and the hinge shaft comprises a protrusion on an outer circumferential surface thereof over the top surface of the movable leaf, the protrusion protrudes by a distance to allow the protrusion to be placed on the top surface of the movable leaf, such that, when the moveable leaf is rotated to set the door in the closed position, the protrusion is placed on the base surface, and, when the moveable leaf is rotated to set the door in the opened position, the protrusion is placed above the step-down surface, wherein, when the door is opened, the base surface slides under the protrusion while the movable leaf rotates along with the door, and then the protrusion descends toward the step-down surface by gravity to be located above the step-down surface, in a position lower than the base surface, the top surface of the movable leaf further comprises a vertical surface defined between the base surface and the step-down surface, and a rotation of the movable leaf in a closing direction of the door is blocked by the protrusion located upstream of the vertical surface with respect to the closing direction of the door, so that the door remains in the opened position, characterized in that the door hinge assembly further comprises a stopper unit disposed between the stationary leaf and the hinge shaft and arranged to control a distance by which the protrusion descends towards the step-down surface, wherein the stopper unit comprises a step extending from a wall surface of the stationary leaf facing the hinge shaft and a protrusion protruding from the outer circumferential surface of the hinge shaft, the protrusion of the stopper unit being allowed to be placed on the step of the stopper unit, when the door is set in the opened position, and wherein a distance between the step and the protrusion of the stopper unit is smaller than the difference in height between the base surface and the step-down surface of the movable leaf, or smaller than a distance between the protrusion of the hinge shaft and the step-down surface of the movable leaf, as seen when the door is set in the closed position.