Hidden door hinge

A hidden door hinge comprising:

• a fixing piece having a ‘C’ shaped bent structure and being fixed to a hinge installation part of a doorframe;
• a rotating piece comprising a hollow on one end and an axial pin connecting piece on another end, an axial pin connected to said connecting piece and serving as a rotating support axis, the rotating piece is inserted into the ‘C’ shaped bent structure and pivotally connected thereto by said axial pin of the fixing piece;
• and
• a ‘L’ shaped door leaf connecting fastener having a connector joined to the door leaf and a projection extending therefrom and being inserted into and adjustably connected to the hollow of the rotating piece,
• wherein the hollow of the rotating piece is an opening extending in a vertical direction, two first adjustors are adjustably connected to respective upper and lower ends of said hollow to engage said projection, and the vertical position of the projection relative to the hollow is adjusted by said first adjustors, such that the height of the door leaf is adjusted, wherein
• the rotating piece comprises a first bent portion, which is a short bent portion in which the axial pin is located, and a second bent portion, which is a long bent portion in which the hollow is formed, and wherein
• a through hole is formed in which the axial pin is inserted in the connecting piece, and a threaded through hole is formed in the middle of a sidewall of the second bent portion, and a bolt is threadably engaged with said threaded through hole for fastening the projection inserted in the hollow.